That's fair, although I wasn't really saying that Smith would cost great prospects -- just that the Giants probably wouldn't target a guy like Cave in return for him. I'll note that Smith's salary is lower than Familia's, and he's also left-handed, which could help his market. Also MLBTR even noted that the prospect haul for Familia seemed light, and the Mets were between GMs at the time, so maybe it's not the best benchmark: https://www.mlbtraderumors.com/2018/07/athletics-to-acquire-jeurys-familia.html But yeah, pure rentals ultimately shouldn't cost too much. It might come down to something like what you propose (Yunior Severino) but I wouldn't expect the Giants to jump on that deal too early, and there's no guarantee that offer would win out either (other teams could offer similar prospects to Severino, and then it would be almost a coin flip to see which prospect the Giants preferred).