I think Nick Chubb's contract is the best an RB can hope for these days. 3 years, $36M, $20M guaranteed.
Even at $12M a season, I don't think the Browns mind paying him at all. He doesn't get recognized this way, but IMO Chubb is a generational rusher. He has somehow put up 5 consecutive seasons over 5 YPC, and hasn't had a ton of help.
King Henry is the other RB I would start using the term generational with, and his 4 year, $50M deal is in that same ballpark as Chubb. The Titans got their money's worth for the first 3 years of that deal, and even then, they really want out for year 4.
These second-contract RBs really want something like Christian McCaffrey's deal (4 years, $64M, $38M guaranteed), or Zeke's deal (6 years, 90M, $50M guaranteed), but those kind of offers just aren't on the table any more. Every team that's signed an RB to a contract that size has ended up regretting it. The Chubb and Henry deals are about the most a club can live with