Hard one this because as soon as you mention STL you are into 3D cad and 3D and cheap can't go in the same sentence.

What used to be Alibre is now Geomagic and their PE [ Personal Edition ] Which is now called Cubify, is £175 plus VAT in the UK but if you contact Geomagic in the States they will sell you a copy for a lot less or at least the same in $$.

Ring them 001 800-691-1839 and explain about being a student as I know there is a student discount and I'm sure it can be upgraded later.

Best to talk to the US in person.

I have the Pro version and saved about £600 dealing with the States.