Cave also had a .363 BABIP last year.
Smith is a pending FA but he is well regarded and pitching great right now. A LHP who dominates both sides. He might be the Giants best trade chip, so I think they need to aim for upside on his return.
Don't get me wrong, Cave is a useful player and the Giants would benefit by having him. But they can't spend Smith to get a guy like that, or their rebuild will go nowhere -- they need to find their Cave types just like how the Twins did (DFA and minor trade situations).
The Giants "trade chips" aren't actually very good ones because MadBum and Smith are half-year rentals. The market prices, as long as the team is really willing to deal them (sounds like may not be the case with Bumgarner) for these types of guys are not really high (see Familia and other deals from last year).
In my opinion Smith should cost a prospect in the Twins range of 10-20. MadBum a little higher or multiple 10-20 guys.
I'd propose Yunior Severino for Smith. Rooker for MadBum -If they want a pitcher Jhoan Duran. Piece that together however you want for both and maybe add in someone like Jose Miranda.
The highest guy I'm offering for any rental, no matter whom (including these two in one package), is in Trevor Larnach's range, and they wouldn't be getting much of anything more after that if he's the target.
(My current top 10 would go something like: Lewis, Kirilloff, Graterol, Javier, Balazovic, Larnach, Duran, Rooker, Thorpe, Enlow)
Honestly though, in the Twins current situation (1 starting pitcher under contract for 2020?) I might be shooting a bit higher for guys with control for this year and the future. So now we're starting to talk prospect names people might not like, as in Graterol, Javier, Balazovic, and possibly even Lewis/Kirilloff if it's the right guy (not sure who that would be at this point).
Scouting Report: Power: 30, Hitting: 50, Arm: 60, Defense: 45, Speed: 45. "Line drive swing and shows good contact and on-base abilities. Double's power at his peak. Strong arm from 2B or the OF, stiff hands. Not a fast runner, but above average instincts on the bases. Skinny body doesn't look the part, but will sneak up on you. ACL surgery sapped much of his athleticism." (Probably)