I own a graphics business (but I don't really have the equipment to do boats or large graphics). 95% of all vinyl graphic applications are done in solid colors. What you have designed is beautiful but the detailed colors and blends of the mermaid will require large scale printing and contour cutting on vinyl (which is very expensive). An alternative is to have someone airbush the color on white vinyl - durability and UV resistance would be critical. For a printed graphic 7' X 2.5' like you have attached would probably run you around $200 - $300 each but if you can find a way to reduce your color requirements to solids and simple blends it can be much less expensive.

Simple blends can be accomplished with a can of Krylon and will last quite a long while. For example, I created the graphic below for my boat from solid colors and created the blend with a simple can of spray paint. This one would probably cost you $50 - $75 for a pair.