If you go before British Summer Time, it's free to go in formal gardens. Nice on a warm spring day. Otherwise they cost £4.60, which is a rip off. Maze is £3.50 and is frankly a bit crap but I guess as it's famous you might as well do it once.
Not been in the house, but if you stump up the rip-off £14 to get in, you can visit the house and gardens at no additional charge.
My advice:
visit on a nice March day, park in Bushy Park (free currently but they want to start charging), see the deer, visit the nice playground there (again, nice day needed, as there's a sandpit), then walk across have a stroll in the gardens.
If you've got stamina, from the formal gardens, you can head out on the right side of the Long Water, over Home Park (lots of parakeets and a very old oak) to the Thames, along to Kingston, then back through Bushy Park. I think it's about 4 1/2 or 5 miles.
Otherwise just walk straight back to Bushy Park from Hampton Court