If you're in this business for the long haul, a mounting press is not a short term buy -- it is a long term investment. Avoid buying a machine that will be inadequate for your needs in a few years.
A hot/cold vacuum press of at least 40"x60" capacity is your best buy long term, as it would handle nearly any needs you might encounter. Used ones are sometimes available. These machines are durable and not maintenance sensitive. If it's clean and undamaged, it probably will run for a long time without major repairs.
A Seal 500T mechanical drymount press would be my next -- and last -- choice. They're also durable, and would drymount nearly as well as a vacuum press, if used it properly.
Avoid a small press. Used ones of, say, 32x40 capacity are widely available, and much cheaper than full size presses. That's because every retail framer who buys one soon wants a bigger press.