A minimum of 30,000 tickets need to be sold for the main prize to be given. If less than 30,000 tickets are sold, the winner will receive a cash payment amounting to 50% of the total ticket revenue generated for this competition.
So if you sell 100 tickets, each ticket holder has a 1% chance of winning £500 from a £10 stake, so the expected monetary value of a ticket is only £5. That's a worse return than the national lottery. And it's not much better if the raffle goes ahead even if your valuation is accurate (and worse if you take the £140k).
Good luck, OP, but I think this model only works for Omaze because they spend a lot on marketing and make the houses look very desirable so no one thinks through the maths.