All the costs I am providing are based on the engine being a solid E condition. One that is marked up with some chips might be as little as half these prices.
If you want link couplers then a 370 GP7, $100; a 360/64 Santa Fe PA/PB, $200. A 405 Silver Streak PA, $200.
There are far more knuckle coupler diesels to choose from. A 371 GP7 would be about $125. A 466 Comet PA might be found for $125. A 472 Santa Fe PA might be $175. A 497 New Haven PA would be $200, the 494/95 NH, or NP PA/PA set would be $500.
From there the diesels start to get more expensive. A 372 UP GP7 would be $200; the 374/75 T&P GP7 would be $300; a NP PA/PB/PA set would be $700.
Remember these are upper end estimates for E condition engines, VG condition would be about 2/3 these prices. There are some frequent sellers on the MTF, perhaps one of them has more accurate pricing info.