Emily, here is my cost breakdown of the set up on my 29g:
29g Tank (not reef ready): $50.00 (ish, I think) - Petco
10g tank (for sump): $12.00 - Petco
AquaC EV 120 skimmer and Eheim 1250 return pump - $200 - MR
PC ballast, endcaps, reflectors, and 2 used actinic bulbs - $30 - MR
New PC 10K bulb - $55 - NWA
Timer/powerstrip- $30 - Petco
2 powerheads, crushed coral (don't recommend), B-ionic 2 part and nets - FREE - Craiglist
30 lbs LR - $90 - MR
flake and pellet food - $10 - MR
RO/DI - $100 - ebay
PVC fittings/Tubing/RO hookup - $60 - home depot
Wood, nails, braces, and other tools - $100 - lumberyard
test kits (ammonia and pH) - FREE - frag swap
Nitrate, Phosphate, Calcium and Alkalinity test kits - $60 - various LFS
Salt bucket - $25 - petco
I think those were most of my startup costs.