No direct experience with eGPUs myself, but as I understand it you’re having to buy the GPU itself plus a Thunderbolt enclosure*, plus a Thunderbolt card if you don’t have TB capability already. For the multi-hundreds of dollars spent on an enclosure, you might get better value for money for a separate ex-government PC from one of the usual sellers + a GPU slotted in once it arrives.
I’ve always had the impression that the eGPU stuff was a bit janky and never really caught on given the requirement for a Thunderbolt capable PC*. For the cash outlay, a new (second hand/ex lease etc) PC is probably a far better starting point.
Having said all that, if you’ve got relatively modern machines (i.e., 6 months old) then experimenting with some of the smaller models without a dedicated GPU isn’t going to be an issue at all if you just wanted to tinker with them before committing the cash.
Cheers
(*or a nest of breakout boards from miniPCI-E and probably extremely limited number of lanes and heavily constrained performance as those slots were only ever meant for a wifi card etc.)