I would recommend a Juki 98 Q . It is a workhorse of a machine. No fancy bells & whistles but if you want a good basic, hard working machine with a good size harp, then this is it. Only sews forward & reverse but will sew thru 10 layers of denim (I tried it & it does). It runs about $1100.00 here in Canada so you can get it for less in the U.S.
Best of luck in your search.