Soulcalibur IV

You will need to get around 3,000,000 gold in order to buy every weapon and piece of equipment.

You will get gold from beating arcade and story mode, winning ranked matches, and completing levels for Tower of Lost Souls. To save money, you can unlock items by completing certain tasks in the TOLS levels.
In order to buy all pieces of equipment, you have to unlock a certain number of achievements (I believe 25 or 30). Accessories (items for the guest characters, Algol, and Star Wars characters) might count towards this achievement, but I can't confirm that. A special note: Voldo has a piece of equipment that can only be bought when editting him or a character modeled after him. You have to buy all equipment for both genders as well.

In order to be able to buy every weapon for each character, you must beat the game with each character in story mode. Pretty much, beat story mode 32 times (one time for each character).

There's an exploit to gain some fast gold. On level 60 of TOLS, simply walk back towards the ledge and let Algo knock you down. When de you're down on the ground, don't touch the controller. If your character is angled correctly, Algol will ring himself out and you'll have 12500 more gold. Repeat as many times as necessary.
To make things easier, organize how you'll buy things. Set out to buy all male equipment at once (on Voldo), then all female equipment, then buy all weapons for each character one at a time (So, buy all the weapons for Siegfried, then all the weapons for Nightmare...etc etc).

EDIT: Since Izibaar requested, it should be noted that going through the story mode with every character and completing arcade mode a few times will net you around 1,000,000 gold. So you can get a decent amount of gold in your bank (as well as all of the weapons unlocked) before you go about doing the TOLS exploit.

To add to the original solutions for this achievement I want to clear up and cover a few things that were not made clear.
Make sure you not only complete Story mode w/ all of the characters, but also on the create a character you need to go all the way to the top right of the selection screen and click up the “star” for the remaining generic 5 characters and beat story mode w/ each one of them. Then purchase each of their remaining weapons.
Which leads me to this- if you are unsure who you beat story with, and in order to prevent you from beating it w/ the same characters for no reason go to create a character, then look at each of their weapons listing. Each character should have exactly 8 weapons, no more, no less.
If they have less than 8 then you have not completed the story mode with them.
To make sure you bought every weapon and equipment I just started from top to bottom. Everyone will have their own method; however I found it easier to start from top to bottom for each line of characters.
As someone mentioned about how much money you will need to purchase all the items, it does not take nowhere near 3million dollars. I say just over 2.1 or 2.2mill if that.
Best way to boost as already suggested for money is to go to Level 60 on TOLS and let Algo knock you down close to the edge. Just position yourself to the edge and watch this fool combo himself right out of the ring with a jump flip. Very funny, and never gets old to watch, …. well, maybe after viewing number 45. Good for 12,500 everytime in cash.

To get this achievement it is going to cost you countless hours but continue to rinse and repeat and you will have it before you know it. ;)
P.S. this is my 1st ever Achievement Guide on truachievement.com. Great site. Extremely helpful for achievements w/ suggestions and youtube videos.

I just want to say that despite the patch on Algol not ringing himself out it is easy to simply clear your cache / delete the updates and do that same method offline to get gold and then save and pop back online to pop the achievement online so you can have the timestamp if that's a big deal to you or just unlock it offline too. Hybrid sums up this level 60 "exploit" pretty well refer to his guide. I'll sum it up quick though, let him knock you down near the ledge, stay down and let him throw himself off the stage. For a detailed guide simply refer to Hybrids guide.

EDIT: Apparently the patch didn't 100% fix Algol jumping out of the ring, IXCrucifixionXI confirmed you can still get him to jump out. This may or not be due to the fact he was using a smaller character like yoda I'm not 100% sure I'll have to get up to that point once again and try it out.

Also forgot to mention some items people may forget...
1.) Make sure you complete all story modes as that unlocks two weapons for each character that are required.

2.) Voldo has a mask you can only buy while customizing him so make sure you purchase this.

3.) The treasures do count that you equip on to default characters, so make sure you get them for that 20 G achievement before going for this.

If you have any other tips you would like to see feel free to comment and tell me how to improve!

This achievement is the one you'll want to leave for last. This is because there are two ways of obtaining certain equipment.

The first is to unlock them by finding them in the Tower of Lost Souls, and the second is by obtaining a certain number of achievements or 'honours'.

You should have unlocked all equipment after obtaining 30 honours. So for example, you won't need to get to floor B40 to get the Voodoo Crown; you'll have it already. I found doing the other achievements to unlock the equipment, to be easier than trying to get all of the treasures in TOLS.

For the weapons, play through the story with every character, including the special ones, this should unlock all of their respective weapons.

Play through arcade mode or TOLS to get more gold should you need it.

In the event you do not get the achievement, check each character's weapons again to ensure you have purchased all of them. This was what fixed it for me.