You cannot add an anemone until the tank is stable...which typically takes 9-12 months.
Live rock runs from $3-$7 a pound (going from various prices I've seen posted and come across myself), and you'll want 1-2lbs of LR
per gallon (so at least 30, up to 60 lbs. 45-50lbs will probably look good)
You'll need an araganite sand substrate, probably 40lbs minimum.
The live rock is your filter, so instead of a mechanical filter, you'll just use a couple power heads for water circulation. YOu need at least 10 x per hour, or 300gph for your tank, of circulation. I highly recommend Maxi-jet power heads.
Sicne you mention an anemone, I assume you want a full reef, not just FOWLR
...that's going to mean a good skimmer (CPR bak-pak 2R or an Aqua C Remora), and stronger lighting (at least 3 watts per gallon...i'd look at 2x55 or 2x65 watt power compact lighting).
You're probably looking at $400 for live rock ($150), sand ($40), power heads ($30), skimmer ($100+) and lighting ($100+).
I didn't include optional stuff like a sump or refugium.