For interior cushions, we went with a Sunbrella fabric. Not sure how many varieties and colors of the stuff is availible since the patent has worn off. I am remembering over 100 colors and prints from just one supplier. Prices range from $20 a yd to over $150 with some very intricate designs.
Foam comes in many forms too. From soft to more firm, cost also vary's.
Not sure what is used on the cockpit, other than a closed cell foam would be best to not soak up water, along with a breathable waterproof material.
If you have it done, plan on a few dollars. For my 30', it was close to $12K. BUT< we did not go cheap. It probably could have been done for as little as $8K, but the forward Vberth where we sleep, we went with a 5" instead of 4" foam, Formed
seats instead of flat in the salon, so the foam needs to be cut, buttons, and piping. All add $$ to the overall cost! Material was around $30 per yd.
marty