A sturdy DIY rack can indeed be a surprise in cost once you get rolling at it.
If you don't need yours mobile, here is a bit of a MacGuiver job I came up with at my cousin's spot who wanted to hide his AV gear in a closet.
Instead of a $800 to $1000 metal rack, we ordered something similar to this 7' relay rack
for less than 100 bucks at the time.
Because it's the front of a rack only, we found about $50 worth of brackets, bolts etc. at Home Depot that screwed into the front holes, even though that is not what they are really intended for.
For rear support, we cut 1"x1"x19" lengths of my scrap wood (free) and mounted them horizontally on the rear closet wall to match the height of the front brackets.
This gave us both front and rear supports to lay down some left over & some purchased, plywood cut into shelving to sit the gear on. We used more small bolts and screws to secure it all in place so the shelving did not move and, in turn, kept the front panel from tipping over.
I also (and this could be done a lot rougher) made a template for my router and made a long rounded and tapered cutout section in the back of each shelf so that cables could be run up and down the complete length of the cabinet. Finally I used my drill press to make a bunch more 3/4" holes in the shelving for added airflow.
We cut out sections on the top and bottom of his closet door and rigged up 4 inwward facing PC fans ($2.50 each at Princess Auto) at the bottom of the door and 4 outward facing ones at the top of the door. Just screwed them into the back of the door. We used an old PC power supply from my junk pile of PC parts to run them. Some splicing and plug robbing from other old parts was required. It's a cool basement and probably din't even need this, but we wanted to prove our beer inspired cooling concept.
I also cut and routed some nice trim to frame up where we cut holes in the door so it didn't look like such a hack job. He painted them to match the door.
Probably cost him about $250 in total (not counting his IR blaster) and cost me some old scrap wood that I normally save for bonfire season. We had lots of fun though and it's still working out nicely for him.
The only hack piece left....
He promised me he would move a power outlet (or two) into his closet to run everything but it's been a few years now and he still has 2 extension cords jammed under the door.