I went to the l;ase sturgeon deal Joes put on in Portland and was watching them clean them outside. Listening to them talk my guess is a good reel to start with would be either a 6500 or 7000 ABU. I have the 6500 ABU but bought a larger reel just for sturgeon and it's a set that worked well in a bosat, don't really know how well it would cast. Have only gone sturgeon fishing one time and got twelve of them, all undersized. Leads me to think the 6500 might work well. I don't know if you can get it under $100 though anymore. Tell you a reel I tried for channel cats that I think works as well as my ABU's is the kastking Rover 40. Smallest of their round reels. I think they only have two and the other is the Rover 50. Luck with it makes me think a Rover 50 would do the job. I say that because biggest sturgeon I got was only about 34" and small one was about 30". The really big ones seem few and far between! Rover 50 with say 50# braid should work fine. Found out a bad thing with braid and level winds though. It get's wet it seem to have a habit of digging into the spool and screwing up casting. Might try 50# mono And a heavier weight. Advantage of the braid is it's small diameter doesn't get effected by current as badly. My sturgeon rod has 80# braid but as I think I said, I don't or havent tried casting with it.
My sturgeon set up is an Okuma Classic Pro CL 302L reel wit 80# braid on an OkumaCE-C-701XH 7' rod rated for 30# to 80# line. Whole set up ran me about $75, maybe a bit under, but was several years ago. My brother used to like sturgeon fishing ans his reels were Penn 320,S. Don't know what the rods were. I think fishing from the bank a longer rod would be a great benefit for casting farther. Oh, don't know if you could get a new Penn 320 for under aa hundred dollars either, thus, I suggested the Kastking Rover 50 and that Okuma set up. You might get out pretty good using about a 4oz or maybe heavier weight but you'd need a fairly heavy rod to do it. I'm pretty sure my Okuma rod could handle five of six onces of weight. Have watched guy's fishong sturgeon from the bank around Biggs and their method seemed to be a chore to me. They had an extra very long casting rod and a bucket. They pulled line off the reel and wound it up inside the bucket. Then took the exrta rod and attached the line to the front eye somehow and cast it out, transfering back to the reg rod after casting. Someone else on here might know how they did that, I haven't a clue! I do know when I went, my brother went out into the middle of the river and looked like everyone else did too. Just something to check on.
Good new's, just went and looked and there are a number of Penn round casting reels for well under $100. I would trust a Penn!