Any team that wants to trade for Bell will be looking long-term (3-4 years). No one is going to willingly cough up that much cash to a back (and a draft pick or two) to us for a one-year rental.
So, you have to look at the teams with a large amount of cap space next year as well as their current roster and/or need for a #1 RB this year and next year.
First - the top 10 teams with cap space who could/would make that trade with an eye on their cap space in 2019:
https://www.spotrac.com/nfl/cap/2019/
- Indianapolis
- NY Jets
- Buffalo
- Houston
- Seattle
- Cleveland
- Cincinnati
- Dallas
- Oakland
- San Francisco
Of those, you can remove Cleveland, Cincinnati and Dallas for obvious reasons (same division / no need for a RB)
Colts, Jets, Buffalo, Houston and Seattle would be the teams I'd be most interested in calling. However, Seattle just drafted a back.
Colts - Bell, Luck and Hilton would be a mini version of the Big 3 of Colts lore gone by in James - Manning - Harrison. Colts have a lot of holes, though, so a RB may not be their best investment. Still, they could offer a very high pick (I'd take their #1 pick in 2019).
Jets - Bell is a little older than Darnold, so they'd be looking for another RB once Darnold gets acclimated to the NFL (as Bell would be nearing the end of his career). Likely not an option.
Buffalo - same as above, though the Bills have a #1 RB in McCoy. He's nearing the end of his career, and may wind up missing some games this season for legal reasons. Allen - Bell - Benjamin could be a nice trio in Buffalo. Like with Indy, I'd take their #1 in 2019.
Houston - Bell would put them over the top from possible contenders to solid contenders. Bell - Watson - Hopkins would make a deadly trio. Thrown in Fuller and the Texans would have a solid offense. I'd take their #1 in 2019 and a 3 or 4 in 2019 as well. I'd ask more since Bell would give them more offensively than what they have now and make them immediate contenders.
Seattle - Bell - Wilson - Baldwin would be quite an offense in Seattle. Though their OL sucks *** in run blocking. As such, I'd ask for the RB they just drafted (Penny) and their 2 and 3 round picks in 2019. It makes it easier for me to trade Bell to Seattle since he'd be going to another conference ...and that Washington has relaxed the weed law which means Bell would likely smoke himself out of the league anyway.