If you just want to go out and putter on Lake Shasta  for a day or host a sunset on-lake cocktail party, and all those beds and kitchens in the houseboats seem like overkill, what you want is a patio boat.
These flat-bottomed, pontoon-style boats rent by the hour and by the day, and are much cheaper than the houseboats. Most come with plenty of seating and canopies for shade. Larger patio boats might have barbecues and storage chests as well.
You’re free to bring your own well-stocked coolers, fishing gear, stereo, and friends. Check with your favorite marina  about renting one.