So... I won Hilton Green Park for next March, 4 nights thu-sun! Bidding 80€ in Soho/Mayfair area only, including 4* and 5* got me this, I was pretty surprised actually. I thought it would be more expensive. Was so nervous! Did I get a good price? Now I worry I actually overbid... Oh well, I was going to book a Travelodge if this didn't work out. So yay! I'm not very worried about the (not great) reviews, it is a Hilton hotel, and we are not used to luxury at all.
What did bother me was the taxes. They are a huge part of the cost and it would be nicer if they were included in the bidding price. Overall I paid 399€.
I hope this can help anyone deciding if they want to bid for London hotels. I am happy, and if the stay turns out ok even more so.