Val
MEC makes a couple excellent presses, a Steelmaster set up for 3-1/2 and then add shim plates for your quick change to 3 and 2-3/4 shells. I'd get a 12 AND a 20 press... changing gauge is not real quick and the press are under $200.
All thing are readly available at Precision Reloading or Ballistic Products.
Myself, I have 3 Steelmasters one for 10g 3-1/2 shim to 2-7/8 another one for 12 gauge 3-1/2 and shim to 3 and 2-3/4 another one in 20 g set for 3 and shim to 2-3/4.
Regards,
BallisticBRYAN