I joint a few times the fishing boats of Mr Tu but this is expensive and fishing is crap with all those tourists. Who knows a fisherman or location with a longtail boat for real fishing. Not big game fishing, just fishing and catch a few and fun. Is a phone number available? I have my own gear but a litlle light. 

Best deals are on a long tail boat from the very South, thong krut. 

You need some friends coming along as you have to charter a boat. 

Snorkeling, fishing around Koh Taen, will cost around 3000 for a boat for a full day. 

So around 500 per person.