Visit the website www.betterbidding.com
They have a forum dedicated to priceline and hotwire that can help you figure out what other people are paying for hotels in the city you are visiting, and they can help you come up with a bidding strategy.
You may just have to ratchet up your budget to around $155, or maybe you're SOL. One of the things they told me is that you don't necessarily get a better deal by waiting until the last minute. If business for a hotel suddenly picks up at the last minute, they don't offer good deals on priceline. So really it's a bit of a crapshoot.
If you're just going for sightseeing and you don't mind taking a 30-40 minute subway ride into central london in the morning and out in the evening, you can go to a hotel in outside of central london, just be careful what neighborhood you pick.
There's actually a Best Western in Barking which is a neighborhood in east London which opened up less than a year ago in that has rooms around the $150 mark. It would make a good base if you plan to sleep there and spend your days exploring. My family has an apartment in the apartment complex next door. The neighborhood is OK, but nothing fancy. It's very close to a tube station, and very easy to get to all the touristy spots. Just a thought.http://www.tripadvisor.co.uk/Hotel_R...x_England.html