I would say it depends on what you want the lambs for, really. I am going to pay $90-$110 for St. Croix/Katahdin cross, weaned lambs. I am starting a small flock and want some good bloodlines, so I'm buying directly from the farm. My sister buys all hers as bottle lambs at auction for around $15-$25 a piece. She doesn't know any particulars as to why they are being culled from a herd, if they are sick, full of worms, etc. She doesn't even know for sure what breed they are. She just buys them. Consequently she has had no end to trouble with the sheep she raises and seems to wonder why.
Now, I like a bargain as well as the next guy, but it depends on the purpose of the sheep. If you intend to keep them and breed them or even show them at 4-H, you may want to invest in quality. If you just want to finish them out and butcher, I'd go for the bargain sheep and build them up on your place.