The Blue Book of Pool Cues, 3rd edition, doesn't have any prices for Renis cues, just a single sentence indicating that he's a cuemaker from California. I'm not sure how many cues Renis made, but I've wanted to try one out just to see how it plays.
Since the one listed on eBay comes with two shafts, I wouldn't feel bad spending up to $300 on it. Any more than that and I'd probably lean towards buying a new cue from Chuck Starkey, but then with a Starkey I know what I'm getting.
The Renis cue could be worth as much as $500, according to some posts (see below).
If I recall correctly, there were others who made Dymondwood cues, so you might want to email the seller to ask how he knows or can prove it's a Renis cue.