You can CREATE your own mining pool, and host it urself. Its not that hard. There are templates out there, basicly all you got to do urself is get the server space (which is not much) and mess around witht he code abit (i guess most users involved in crypto could do it). I dont see a reason why you would buy a miningpool unless its already operational with alot of users.
sorry I mean mining rig
Try to get the parts for cheap and build one by your own.
Buying a whole rig may be a) more expensive if the hardware is new or b) be used and the GPUs may die earlier.
However right now GPUs seem to be very expensive.