Just save up till you have a decent budget, why ruin your S2000 with something sub-par to the car and its OEM parts? I was a student too, but with patience and contacts, able to get good stuff onto my car for a modest price, just play it smart rather than oh can't wait then when you fit on the parts, crap I just forked out $XXX and its so crap that I need to fork out another $XXXX. A lot of shops are there to sell you products, they get crap load of profit/commission and not necessarily a good product.

Bilstein PSS9 are my recommendation if you want to make your S2000 even better but that's up to you now.