nez -- if you read the posts here and look on ebay for laser pump diodes you will find that $50 won't even get you started building a green not to mention the test equipment and machine shop tools you will need i recommend buying what you can from deal extreme with all the money you have.
if you want high power read all the posts about building a red burner and please don't ask redundant questions as many here do.
You do not want to build green lasers, it would take too much time. Check out Dealextreme for some cheaper (both price and quality) laser pointers. You can get a "True" 50mW for $50 that will pop balloons and smoke leather.