With PL you specify a zone and * level and then place a "bid". If your bid is rejected and you add a zone that only has lower * properties you have a "free rebid". If your "bid" is accepted your credit card is charged and no changes or cancellations are permitted. biddingfortravel.com is a great resource.
With Hotwire you're given a price and a list of amenities. In some cases you can identity the hotel based on the amenities. betterbidding.com is a great resource.
With Easy Click you're given a detailed description for their off the record hotels. You can almost always identify the hotel with a google search. I believe most of those reservations can be changed.
Some hotels offer a pre-paid non-cancellable, non-changeable rate on their websites.
Some properities charge a resort fee which is extra.