I could be wrong, but I don't think there are any SUNSET DINNER cruises one can go on out of San Jose. After all, if it is after sunset that would mean driving back to SJ after DARK, which certainly can be done but it is not the best way to go. OTOH, if you are staying in Jaco or Quepos or some other beach town, then that is not a problem.
If you don't mind going on a really nice cruise during the DAY, then the "Calypso Cruise to Tortugo Island" is highly recommended (
http://www.calypsocruises.com). It leaves from the port of Puntarenas and runs about $99 (+ a new $5 fuel surcharge) with or w/o transportation from SJ, Jaco or MA ($10 less for ticas).
JD Watersports out of Jaco offers a sunset cruise (with snacks and refreshments but no dinner) and their webpage says "Transfers from San Jose, Puntarenas, and the Jaco area are also available" (
http://www.jdwatersports.com/sunset.htm). That tour runs out of Los Suenos (north of Jaco) from 4-7PM and costs $49/pp (not including what they charge for transfer to/from SJ).
The one sunset DINNER cruise that I have found confuses me a bit. It is this one:
http://www.manuelantoniopark.com/mapk/english/sunsetsails.html. Their webpage doesn't give any prices but states the sunset cruise starts at 1:30 in the afternoon and runs for 4 hours. That would mean that the sun would actually be setting just as you get back into port. You might get a little "sunset action" out in the open water but most of it would happen while you were returning or actually back on land. Their ad copy also says "On the sunset sail, after dinner, you may view one of the often-spectacular sunsets. It is truly a romantic ending to a memorable day in paradise." this would mean that you actually would be having dinner during the mid to late afternoon rather than at sunset or in the evening. None of that is to say that the cruise is still not worthwhile. I'm sure the food is pretty good and you get to sun and swim, watch for dolphins etc., but I would like to know a lot more about it (especially including the price) before I would sign up for it. The last bus back from Quepos leaves at 5PM so you'd have to find your own way back if you wanted to try and do this out of SJ.