Many good deals are out there on used equipment. An older all solid state HAM HF rig can be found for $300-400, in fine working order.
Amp draw will depend on how much power you are transmitting, as this is adjustable on Amateur radios. Max power out is typically 100 watts, most will draw 10-12 amps at full power. Many are designed to run on 12 VDC.
The setup is kind of specific to location but in general, on a boat I would expect a good wire antenna (either home built or commercial) and a good automatic antenna tuner. This can be terribly complicated or relatively simple, it just depends.
The best advice is to get some help from local folks. Clubs are a great way to share skills, seek advice and get help deciding on what gear suits a particular application the best.
I have found there are mostly two types of HAMs, at least around here. One group are the absolute expert operators, the contest winners. They have talked to seemingly everywhere on Earth and can get through in the toughest of conditions, including contest pile-ups.
The second type are the tinkerers. This group builds their own antennas and gear. They have a pile of parts and spend time building gadgets for their hobby. Many build radios and gear just because they can.
Like Auspicious, I was a Tech+ N8TIH, then earned my General and Extra, as NI3S. Before all of it a commercial license became a necessity. It is still valid and has come in handy from time to time, although it is not required for my current vocation. The commercial license does offer me operator privileges on SSB so at some point that may be a good thing.
Good luck to all that seek to earn a ticket.