You can't predict when you will get the best deal on Priceline. It just depends on how full the hotel is and how much inventory it has turned over to Priceline. Just remember that Priceline rooms are non-refundable. If your travel plans change, you pay for the room anyhow.
Yes, you want a 3* at the port. This will get you a Holiday Inn, Hilton, or DOubletree. The hotels are actually in Cocoa Beach, a short drive from the port. The shuttle is $3 per person, or you can take a cab. Before I start questions, the Radisson at the port has a free shuttle, but Radisson is not a hotel available on Priceline.
Most of the time, you can't get Priceline until 6 months or less before your travel date. You get the best deal when they have a lot of inventory that they don't expect to be able to fill. Thus, holiday weekends, you will pay more than slow season. 3 days before a trip, IF they have a lot of open rooms, it will be cheap...but they might not have open rooms.
A suggestion--make a cancellable (is that a word?) reservation somewhere. Then bid Priceline. You know that you want to keep your bid below what the reserved room will cost. Farther out, stick to your guns and don't bid too high. You can always go higher as your date approaches if need be.
We usually bid 1 week to 3 months ahead. I haven't noticed a lot of price variation (like maybe $8-10 difference per night) as things progressed. The best "deals" are the right near the date ones, but you can't count on those.
For this cruise...I'm paying $34 for a holiday inn that lists an internet rate starting at $98 plus tax. My total, including tax and Priceline service charge is $44.31. SO...I get a nicer place for the cost of a cheapie or less.