How much would it cost me to either build or buy a decent computer to play WoW? I don't need to play on ultra or anything I just need a decent starter computer with no lag or at least minimal lag that I can upgrade later.
WoW doesn't require a lot to play.
I would look at Microcenter.
Coolermaster Case with 500W PS - $40
i5-6600k with Motherboard: $265
8Gb Ram: $60
GTX 1050ti 4Gb: $140
1Tb HDD: $45
$550 for a pretty solid 1080p gaming rig.. and upgradeable down the road.