I would also add my vote for having one press for each gauge. I have a MEC 600 jr that has loaded lots of 12 ga and still works great. I bought .410 dies for it, but changing them out is really a pain, especially if you only want to load 2 or 3 boxes.
Single stage presses like the MEC 600 jr are easier set up and adjust.
If you buy a used one, check the inside of the dies to make sure they are not coated in rust.
If you shoot a lot, reloading can be fun. You can customize loads for the task at hand. I was able to crank out some very light 7/8 oz target loads for my boys when they were smaller so they could enjoy shooting the 12 ga. Now their wives enjoy shooting the same light loads
Here are some current 12 ga light target load prices that I found after shopping around a bit:
25 # lead 8 shot = $37.00 (400 1 oz loads or 9.25 cents per shell)
4 # Red Dot powder = $45.00 ( 1,647 shells @ 17 grains per shell or 2.7 cents per shell)
1000 primers = $29.00 ( 2.9 cents per shell)
500 wads = $9.00 ( 1.8 cents per shell)
I figure the hulls are free.
Total is about 16.65 cents per shell or $4.16 per box of 25.
Hopefully I did the math correctly
trapshooters.com has an online calculator that you can play with.