Ultratron

I was able to pop this somewhere around level 48 I believe. I made sure I always had 2 shields and 3 smart bombs at the start of every level. It's not necessary though. The rest of your money should be spent on upgrading all the pets, scan range, and level up. Some may suggest dot slurper upgrade, but I did not find it necessary. I recommend buying the level up first and getting the one time fee of 5,000 out of the way. The beauty of this, is the more you upgrade your pets, the less work you have to do. Strafe around the level shooting, and you will find they do a lot of the work for you. Remember, every 10 levels you get a checkpoint, so eventually you will prevail. This is another achievement that sounds a lot tougher than it actually is.

You need to upgrade the shooty, laser, rocket pets and the scan range to the max.
To do this with ease start from level one and upgrade nothing but your pets and the scan range. Complete every level without losing any shields so you do not have to spend money on those. There are assault rounds every ten levels starting from level five (5,15,25,35,45...). Make sure to have at least two bombs to make your way through them without too much problem.
Once you have money to buy an upgrade, purchase it but prioritize getting the other pets instead of having one pet maxed, this will help you tremendously as the pets will be doing pretty much everything. You can restart the level if you have lost a shield by leaving the game and continuing, as soon as the game starts you will be in the level you were at the moment you have left the game. You will get the achievement between level 50 and 60 if you have followed this method.

In summary:
- Start from level one.
- Do not lose any shields, restart if that happened, doing this will save you tons of money. You can always pick up the shields that the spiders drop so you have more than three shields when fighting against the bosses. But, no matter what, it is not recommended to go out there with less than three shields, as sometimes you could be hit multiple times at once not giving you the time to leave the game.
- Upgrade and buy nothing but your pets, the scan range and two or three bombs before the assault rounds and only for those. (As completing an assault round without being hit could result very difficult).
Good Luck!

If you follow my solution you should be able to unlock this around level 60 (probably sooner). I unlocked the achievement at level 58 and i know there was still room to be more efficient.

To be honest with you guys. I had a hard time to survive around level 35 and i figured out the reason. I didn't want to invest in bombs and i only invested in the pet based upgrades, but that was a mistake, because you can't rely on your pets all the time. I know using bombs could make some levels easier, but it's also the reason why some players unlock the achievement with a high level. They bomb there money away.

My suggestion:
Upgrade your droid strenght 2 times for 3000$ total as soon as possible. It gives you enough power to kill enemies way sooner and even at level 50+ i had the feeling to be strong enough to handle all situations. If you kill your enemies too slowly, they will fill the field and knock out your pets and give you a hard time evading all the shots. After raising the strength everything was so much easier and i was able to protect my pets most of the time.

Upgrade your dot slurper skill for 1500 $ a single time. That's also something you want to have as soon as possible. I did this at level 30 and i think it was also little bit too late. This skill is worth the money and helps you to collect money more easily... especially if you don't have much time to collect stuff, like in the later levels with many enemys.

With these upgrades you should have no mayor problems. Don't waste your money for bombs! It can't hurt to have always a single one just in case, but you can beat all levels without bombs. I prefered to have 3 shields instead of 2, because in some situations i lost health very quickly. So i restarted every level when my shield got below 3, but that's your decision. Better safe than sorry, if you ask me.

Another thing you probably already know: Completing the bonus stages with 100% gives you 1000$. I found the dodge stage easy to complete and i always did my best to grab the extra money in this kind of stage.

That's all i have to add and please note the whole solution is only one suggested way. Of course you can do your own experience in upgrading other stuff, depending on your playstyle.

If you still have a question, feel free to leave a comment. Good luck!