I got a sheet of MDF at Home Depot for about $15. They cut it into five 18" x 22" pieces for me.
I bought the three 36" 5/8" steel threaded rods at HD for about $5 each. Toss in the nuts, washers (I didn't bother with the rubber washers - all steel). I used my $20 cordless drill to drill the holes, then spray painted them black and assembled it. Easy easy.
BTW, MDF soaks up a lot of paint. If you plan on painting it, paint a primer coat and plan on at least 3 full coats with some sanding.