I aswell dont have very much money...I also have a 30 gallon tank. What I did was about 3 months ago I bought about 7 lbs of live rock. and about 5 lbs of lavarock. The live rock was $4 bucks a pound @ my LFS. Dead rock will become live rock over time. I have some coralline algae growing on my lavarock now. So you don't have to buy a whole lot of live rock. Start out with under 10 lbs and some dead rocks. If you buy it online you have to pay a hefty shipping fee usually.
one warning though:
Adding live rock to a cycled tank can cause minicycles and stress out fish.