Well perhaps not a minefield BUT-
If you take the marine HF option here in the UK you licence the boat as a marine station-totally free and takes a few minutes online and open to any one from anywhere so long as you have a UK address-believe its the same in the US?-what you get is a call sign unique to your vessel.
To use the radio to transmit you then either need an internationally recognised long range operators certificate;or to be supervised by someone with one;or an internationally recognised full ham licence with permission of the vessels captain.
These regulations or any breach of them are applied by whichever country your vessels radio station is registered in.
As far as I am aware you can transmit on any internationally agreed channels so that includes marine and ham.
If you have a marine hf radio however new ones tend to be preprogrammed push button affairs set up for marine channels. You have to modify them to transmit on Ham channels-no problem other than if you happen to be a boat from Europe there are several Ham chanels popular with US sailors that are unlicenced over here so technically if you mod the radio to access these if heading across to the US /west Indies you are committing an offence under European leglislation.
Likewise several of the Marine Icoms popularly used in the US do not have DSC fitted-again illegal in Europe.BUT your radio details are not taken as part of licencing info.If you are a US boat operating in Europe no problem as leglislation only applies to European vessels.
Which nicely brings me to Ham radios.
It is illegal under international agreed and locally applied leglislation to modify a Ham radio to transmit on all chanels IF you are a land based Ham operator. However if you are operating from a Marine station-on your boat-as far as I can gather with a full Ham licence or Marine long range operators licence or under the supervision of long range operator you can transmit on marine chanels so the offence becomes somewhat vague in my opinion..
Last but not least in the event of a real emergency international agreement allows anyone by any means to summon help without threat of being prosecuted for an offence.
Confusing or what!
As for cost both here and in the US Ham training takes you through 3 stages to full licence and costs very little. Certainly in the UK and I would guess in the US Long Range marine operators certificates tend to be run by nautical colleges and are aimed at training comercial operators.As such over here they can cost around about £1000/$1500