Here are some options that may end up being of the "kind of bargain basement, but with some ability" variety:
Tyler Clippard (33): 3.67 era, 1.17 whip, 11.1 k/9 in 2018. Bad in 2017, but prior to that, has been a very reliable reliever. Career 3.16 era, 1.13 whip, 10.0 k/9.
Brad Boxberger (30): 4.39 era, 1.43 whip, 12.0 k/9 in 2018. Volatile. Very good in 2017 (3.38 era, 1.16 whip, 12.3 k/9). Sign him cheaply and hope he's good Boxberger?
Greg Holland (33): 4.66 era, 1.62 whip, 9.1 k/9 in 2018. Obviously a pretty terrible season. But from 2011-2017, he put up this line: 2.39 era, 1.10 whip, 12.0 k/9, and 186 saves, so he has lots of closing experience. Might be worth a flier. Relievers can be up and down and it's clear he has some ability. How much left in the tank?
Alex Wilson (32): 3.36 era, 1.05 whip, 6.3 k/9 in 2018. Not a strikeout pitcher, but he's had a solid career as a reliever: 3.23 era, 1.19 whip, 6.0 k/9.
Justin Wilson (31): 3.46 era, 1.43 whip, 11.4 k/9 in 2018. Strikeout pitcher. Not a good whip in 2018, but he's been pretty good over his career. Career #s: 3.33 era, 1.27 whip, 9.9 k/9. Lefty who is more than a LOOGY.
Hunter Strickland (30): 3.97 era, 1.41 whip, 7.3 k/9 in 2018. Again, big whip. But his career numbers are pretty solid: 2.91 era, 1.19 whip, 8.4 k/9.
So it's not like there aren't any MLB quality relievers out there still. I don't know that these are the guys you want in the playoffs facing Carrasco, Altuve, and Bregman, but for the regular season, these guys would be perfectly fine I think.