Look locally at your trap/skeet clubs for a used MEC Jr. or put up a WTB ad on their bulletin board. Unless you buy your components in bulk - 8# jugs of powder, 5000 wads, 5000 primers, lead by the hundredweight or greater, there isn't a lot of savings in 12 or 20 until you get into something not commercially available.
As an example, I reload both 12 and 20 with only 3/4oz of shot - neither load is available from a mfg. I get 533 loads from a bag of expensive shot (BigJim will get 400 using 1oz) and mine are very easy on the shoulder and even work my gas guns. I also like to use 8.5 shot - TMK, 8.5 is no longer offered in 12 or 20 gauge ammo, which is too bad because it is the perfect size for 16 yard trap, skeet and sporting targets out to 30 yards. So, in MY case, it makes sense to reload for 12 and 20.