This game is simple in concept, but nice in design. I liked how as you progressed through the different colours, all colours changed, including the lasers.
There are a few things that would be better though, here are my suggestions.
When getting upgrades at the start of the game, it's really easy to get the best stuff up first, thus avoiding any of the previous purchases. I suggest making them more expensive so that people have to work a bit at getting the weaponry, thus increasing the difficulty of the game. Even having the gun as upgradable is an idea, that way you go through all the different purchases, or can upgrade multiple times to speed up the progress. This can also go for the money collector.
After getting all upgrades and purchases, you tend to get a lot of extra money. It might be an idea to utilise more once-per-game upgrades, like the bomb. An item to fully replenish your health and bullets, to slow down the game, temporary invincibility, all are valid ideas, see which one sits with you best.
A few suggestions for fixing. When the laser things are destroyed, sometimes they leave behind part of a laser that still hurts you. Also, it might be an idea to add some instructions, even a one page screen with arrows pointing to most of the stuff, shield power, bullet power and their respective guns, money, distance and other things. This is a great place to sort of 'advertise' your upgrades in the shop.
Also, at the end of the game, maybe having words scroll across as someone passes past the red zone, something like '... I did it...' adds a little more in terms of story, and gives a somewhat more satisfactory ending.
Despite all these things to change, the actual game is pretty neat, and I'm happy to have played it. It's simple but not in a way that makes it look like you made it too 'cheap'. Also, most of the errors are minor, and it seems you caught the worst mistakes early. I'm impressed, and really want to use some concepts you've got in the game when I get good at flash programming.