You could do a beautiful 75g with a marine betta, dwarf lionfish, and a snowflake eel
But they are right, the startup costs will be quite a bit higher than a fresh tank. For one, you will need a skimmer (people will argue this but lionfish are big waste producers) and an RO
unit. You can get away with buying dry rock and cycing it yourself to save some money. I prefer the look of 1lb / gallon.
As for getting stung by the spines, as long as you aren't trying to punch the fish or chase it around with your hand, it shouldn't sting you.
It can be tough to keep water quality under control but not too difficult, especially if you already have experience with keeping fish. Plus, you always have access to us when you have issues