If you're already here, you already have a "visa turista" - for three months stamped into your passport. This happens automatically and is not something you have to apply for via a lawyer. You can extend this visa for three months at immigrations or by leaving the country for Uruguay and coming back in. Try to do it more than once and you may well have problems (nothing really a lawyer can do about that either). A student visa will give you one year and is also renewable (so long as you continue to provide the necessary documentation).
Once you've got your paperwork together (see the immigrations website for info about what you need), it's a pretty easy process to do by yourself. If you do want a lawyer to help you through the process, I'd also recommend Celano - I think he charges around US$ 1,000 for assistance with a student visa (but you'd have to check this...it's been a while since I saw him last) and that doesn't include speeding up your DNI afterwards. I'm pretty sure that most immigrations lawyers charge similar amounts. I heard about other lawyers doing it slightly cheaper - but they aren't registered at immigrations so can only do so much...
