Rock Band 2

Edit 11/7/10

So, two years later I FINALLY unlocked this achievement. I really am surprised that so many people gave my previous solution so many positive votes considering I hadn't unlocked the thing yet. My previous solution speculated on how one could unlock the achievement. Now, here are the facts:
-Anything you buy in the Rock Shop counts towards this achievement.
-The total $100,000 can be spent across several characters.
-The game does not keep track of how much you have spent. You won't know how close you are to getting the achievement until you actually get it.

I made a word document that kept track of how much money I spent in the game. Gaining money in the game is a bit harder than gaining fans, but there are some simple ways of gaining more money:
-Make Setlists in every possible venue and pick songs you know you can Gold Star. The more songs in a setlist, the more money earned.
-Feel free to play the longer, 5-9 song setlists as well. If you know you can 5 star the songs, you'll be in good shape.
-Always take the offers that either double, triple, or quadruple your money, or swap out the last song in the setlist to earn more money.
-Use one of your characters in someone else's band either on a local tour or a Live tour.
-Complete the Endless Setlist (will net you anywhere between $50,000 and $80,000).

Something I did was hired the Spirtual Guru character as soon as I could. His character allows you to have more of the offers granted to you "Double or Nothing," "Triple or Nothing," etc.The Marketing Executive doesn't actually earn you that much more money. The Accountant is a poor choice. Gaining double or earning nothing sounds great, but its really the same as earning the regular amount for each song played. Besides, you don't want to risk doing the Endless Setlist only to NOT get any money from it.

Also, the achievement unlocked for me a few thousand dollars early. It may have been because I didn't do some math correctly, but if you just keep on playing the game and earning money, you should have this achievement in no time.

The venue in Austin, called Echo Hanger on World Tour has a 'create a setlist' with 3 tracks, If you can 5* them all I belive you get $3-4000. This is a quick way to earn some money.

Once you think you have gained enough, (Its easier to buy the essential items and wait, so you know you have enough), Buy all of the expensive Guitars/ Bass Guitars/ Clothes, Easily done.

Just to add onto the previous guides above me, although the achievement says "CLOTHES to the Edge," you can buy ANYTHING and EVERYTHING from the Rock Shop and it will count toward the achievement. Buying instruments will count as well as clothes.

Also keep in mind that you get much, much more money when playing at bigger arenas/stages. Playing gigs at the small places will earn you cash, but a lot less of it. Keep playing and you'll have $100,000 in no time.

This is actually pretty easy if you just forget about it and just play through the tour. Just check how much money you have now and again, I got it when I was about 2/3 of the way through the tour. Plus I recommend waiting until, you have the full $100,000 just to make it easier as if you spend whilst you progress through the tour you'll never know how much you've earnt...

Okay so I just got this one today and this is what I did. I finished all the impossible instrument challenges(which if you five star every song in it you get $1,800) also I used The accountant despite what Hybrid says I never once lost money and here is how. The deal with the accountant is very simple if you 5 star a song you will earn double the cash. Its that easy I know there are a few setlists that can get you $3-4000, all you need to do is go to those and play them with the accountant hired and 5 star all the songs. Forget about playing at a higher difficulty and trying to gold star this works so much better and so much faster.

EDIT: 8/29/11
The Endless Setlist on medium with the accountant got me over $100,000 and I only missed 1 star through the entire setlist.