You can get in to a good used trailer-sailer for under $3000, including trailer. you'd then be sailing and not building. Also, those boats always need some maintenance so you'd be developing those skills as well.
Dogs on the boat. You'd need a lot bigger boat to have the dog and yourself be comfortable. He's not, in general, going to be on deck. He's going to be in the cockpit with you, where you're trying to sail the boat, ie...always right in the way. Not even considering that getting wet while sailing is one thing, sitting hard up against a wet dog for extended periods of time can get old really fast. (g)
I've got a lab and don't even consider it on a 21' boat. If you've driven around with your dog in a pickup truck, with him in the front seat, the experience will be similar, but worse. If he's standing, he's stepping on you-ouch!!! If he's sitting he's in the way, and to move he's got to stand and he steps on you again-ouch!!! Every once in a while i get the urge to take him with us. My wife quickly and forcefully disabuses me of the notion. she's got a problem with wet dogs, i guess. One more item. My dog, and probably your's, loves to swim. Do you have any idea how much strength it takes to snatch a ninety pound dog out of the water when reaching down about 18 inches? It ain't happenin'. Not for you, not for me, not for the Governor of California.(g)
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.