Those prices seem relatively normal, the UK is usually more expensive but I can buy frames for less I guess made in China, however if you want custom mat ctutting then expect to pay that kind of price.
Cutting your own mats is easy so do your own as Ann suggests, and you should be able to get 20x16 frames (inc glass) for around $15-$20 and the board will be around $3 extra if you buy full packs from a framing suppliers (not a framing shop). I can get larger frames lke 24x20 for about $20-$25.
I had a profile cut specially for my own main set of exhibition frames, that actually worked out no more expensive than using an off the shelf profile because I had about 75-80 frames made at the same time. and stained the wood myself. The frame supplied the bare frame and then the backs and glass packed seperately and I bought fittings and mount board direct from a trade framing suppliers.
But go look in your local household stores because the imported frames can easily be half the price of a commercial framing shop. A warning though some of the cheaper mouldings are not wood, the edges sag, bend and are not good, I have found excellent low cost frames in one UK chain and I would have to pay more than double to get frames made here. I use these when selling framed prints.
Ian