You have to pay for the trip the away homeowner takes, you have to pay the utility bill while the crew is there (the electricity and water bills usually double), and you have to pay taxes on the materials used in the room and possibly on the prizes.
To clarify, the homeowner pays taxes on the prizes. They do not pay for the prizes themselves. TLC pays for the transportation of the crew to the site, the labor fees of any cast/crew involved, and the materials within the budget. Sometimes they pay for prizes if no company donates a prize.