30 amp is adequate for home needs. Get a box with the breaker switch in the box. You need a single pole 30amp breaker for the main panel too but the ability to shut off power at the outside box is convenient to prevent arcing on the plug prongs. Just like at the campground, breaker off to plug in and to unplug.
I just installed one 30 amp plug with breaker. Wire was $175 for a 125ft. roll of #6. I have over a hundred foot run so I needed #6 wire. Got the box from Home Depot website, 65 bucks there. Add in the 30 amp single pole breaker and I was at $250 total.
Make sure your electrician properly sizes the wire for the length of run you have and be sure he knows it is NOT 220 volts, it is 110.
