I don't know of a website but I was on a tight budget last year too and I just asked students to bring in makeup (they or) their parents or sisters didn't want anymore including eyeshadow, eyeliner, gel. That donation already yielded quite a few useful items. Perhaps you could ask students/families/parents to donate items.

Give a thought to substances to take off the makeup including make up remover and facial tissues and perhaps some cream as well.

Just want to caution that sharing makeup can also mean sharing germs.  We are cautioned never to use even our own mascara longer than a year because of the fertile environment that exists in the tube. 

Eye makeup especially can be a transmitter of germs and eye disease.  I bought my daughter the Ben Nye student kit and supplimented it with a couple things to beef it up.  It sells for $14 dollars and now I don't have to worry about her having to use other peoples makeup.  I encouraged all our actors to make the investment.  Heck most girls spend that on one visit to the mall.  The Graftoban <sp> kit is good as well

we use q-tips to share lip stick and sponges to put makeup on with no double dipping.  We also encourage clean hands and faces and good hygiene all the time.  I am a middle school drama coach and am finding this discussion board a fabulous resource