Refurbished dells are good super cheap options. I have a couple old optiplexes from 2008 still chugging along. Without skipping a beat. They are easy to repair and upgrade some parts too.
Stay the fuck away from HPs. All ot them. Fuck those dirty bastards. They are the bane of all computer repairs due to faulty shitty hardware. Never trust them for mission critical work. They are disposable cheap computers with very poor build quality. Some people like them, but professionals who know better loath them. Present company included.