Choosing a (old, beater) first hardtail?

Have lots of bikes, but right now all rigid, and basically all my riding is road or hard gravel. Would like to get into some basic singletrack, but probably nothing very extreme (I'm in lower michigan so there really isn't anything extreme). I'd kinda like to pick up a cheap hard tail to add to the stable.

I feel very confident asessing everything about an old bike except for the suspension fork. I've never owned a non-rigid bike and I have no sense for which older suspension forks are desirable and which are to be avoided. What brands/models of for would you choose? What would you look for to determine value? Gas/Coil?

Budget here for the whole project including whatever I need to do to it after purchase (new tires/cables/whatever) is ~150 so i imagine this will probably be a rim-braked 26er but who knows maybe I'll find something juicy.