To give you a rough guide to our findings - flights to places like teh Algarve and the Canaries, etc were coming out as at least £300+ per person (no discount for children) if travelling from London, many a fair bit more. Accomodation about £1000 a week for a sleeps 7 type place, with a pool. Didn't get as far as car hire costs. Our budget for this holiday was approx £500 per person and we were struggling sadly. We were very suprised at how much it was all coming too.
We don't do hotels, etc so can't help with that.
We are taking a 3y, 6y and 7y ont he flight Mind DD has always been fine on long haul, luckily she seems to sleep a lot on plnes.
try one of the holiday parks un UK so the dc have something to do and you get a rest Park Resorts we go to, usually good sites and good standard or accommodation if you go silver or above and loads for kids to do