Welcome to the board Rog. I see you have conquered the avatar mystery, and it looks like you have a rocket in the back ground and perhaps a smaller one in your hand. Happy shooting. Rockets facinate me, and I enjoy seeing the early attempts and progress made by the Germans during the final stages of WWII.
Now a bit about price, size and material. You failed to tell us how large (or old) your family is, but by a 5 wide, I suppose you want more room than for 2 adults. If a stand-up trailer is in your plans, (which may be a bit heavy for your 4 banger Accord) complexity, price and time of construction will greatly be increased. I know for a fact that a tear can be built for about 500 bucks if a cheap HF frame is used, a simple shape is selected, an inexpensive exterior (1/4" plywood either varnished or painted) and off-of-the-shelf hardware is used.
By eliminating all of the bells and whistles, you can make some cost-cutting corners, leaving out fancy galley cabinetry, stove, refer, sink and water tank, sound system, flip-down Sony TV, etc. You mentioned a tear for only one person, and if you are interested in seeing a 6 footer I made, check out my gallery. It has a 40 x 48 HF frame and bed measures diagonally, 6 ft 8 inches. BTW, it only weighs 245 lbs, perfect for a 4 banger, I know, I have one.
I see you are somewhere in So Calif.......too. Give me a hint of your location, we might be neighbors. I'm in Wildomar, and if you are ever down this way, swing on by and we'll share ideas. Good luck.

Roly