Are you talking about this set Brad?
If so, then I'd say it's definitely worth $30, but can probably be had on eBay for cheaper. Doing a quick search for it there, reveals that an auction ended with no bids and a starting price of $20 just a couple weeks ago, and another current auction sitting at $10 with 3 days left. I can't recall what the original retail price was on these boxsets in stores, but it was most likely more than $30!
I've got this boxset, and must say that it's definitely great! One CD for each movie, plus a fourth CD which features outtakes and previously unrleased music from all 3 movies. Mine's in storage right now, but I recall it having a great book of liner notes as well. 4 CDs of great music, which has provided me with many highly enjoyable hours of listening to some of John Williams finest work...
If you're looking for the "definitive versions" though, you might want to go for the Special Edition
CDs instead, though I highly doubt you could get all 3 of these double disk sets for only $30 in a store.
Good luck, but whatever you do, you obviously need the OT music on CD somewhere in your collection, if it's not there already!