Doubt Rubio would command more than 20mil/year. Maybe he can be signed for 16 mil a year for extra year or so. Like give him 3 years/50 mil deal and it is a steal.
I can see him signing something around his current salary. 14M to 15M per year seems about right if he re-signs with the Jazz, while maybe some other team desperate for PG help can go a bit higher, into the 17M-18M range. There will be a pretty decent market next summer considering the cap spike and the positions available.
The top FAs at his spot will be Kyrie and Kemba. Then you have Russell, Bledsoe, Brogdon (not strictly a PG, but still) and Ricky. After that there's an older guy coming off a serious injury like Dragic, a barely adequate starter like Collison, and a young guy like Rozier who was extremely hyped by some after his hot stretch last season but is still pretty far from being a good PG. Pending the trade deadline and the draft with two guys like Morant and Garland who will be picked in the lottery, the Celtics, Suns, Magic, Pacers, Jazz, Heat, Hornets, Nets, Bucks and Bulls will all be looking for a starting PG. The Pistons will also try to get some help as they face the last year on Reggie Jackson's crappy contract, and the Clippers will probably be looking to get another veteran to help Gilgeous-Alexander. That's a bunch of teams and not a lot of talent available, especially with guys like Kemba and Russell most likely re-signing with their teams.
I may not think it's worth it, but I fully understand the Jazz trying to get Conley or Jrue. They're obviously better scorers than Rubio, and they'll also be under contract past next summer. If DL is not sure about Ricky being willing to re-sign (or not being willing to do it for whatever the Jazz offer) then they could find themselves with a worse starting PG next season.