I agree with Noodle, and highly recommend reading the thread she has linked to understand why buying the right lamp is so important.
I would also add that even though you are just starting out and wanting to keep costs down, your lamp is not something you should scrimp on. It is probably your most important purchase and worth getting right from the start. Hopefully you are using a professional brand of gel polish that sell a lamp that has been tested to cure their product optimally. A good quality LED lamp should last you a good few years.
Although it's very tempting to buy as many lovely colours of gel polish as you can, if money is tight to start with, just start with a core collection and spend your money on the right lamp, then you can add to your collection gradually as your business grows. I find clients often say I've got too many to choose from anyway! (And I haven't got nearly as many as a lot of nail techs!) x
