We just went through the same process. We had 4 companies bid for our pool.
The line item costs and products varied widely, but in the end the total pool prices were not that far off from each other. For instance, some companies included salt generation, one a sand filter, one a DE, and another a cartridge filter. Some included 60 ft of gas line, others 100ft. Some included the pool cover, others did not. One recommended a heat pump and the rest a gas heater. Some companies included the topo-survey and others did not.
From what I can tell, there will be a number of extra cost items that may not be priced into the contract that you may need to be prepared to pay. In my case, installation of a dry sump since they hit water, extra gas line footage, extra fill dirt, extra retaining wall since the elevation of the pool was higher than I originally thought. All these costs were estimated by the pool company so I was not suprised, but are technically not in the contract for the pool.
Even though this intially seemed confusing, I was not really that concerned with the prices for each individual component since in my mind the total price of the project and reputation of the builder is all that really matters.
I went to see a few jobs, talked to a number of people who used the various companies then made a decision.
Lastly, read the contract very carefully. There were a number of things I wanted changed or added to make me feel comfortable about moving forward with the project. I am not a lawyer, but was able to work through the contract. Make sure you understand it before you sign it. I've read a number of posts that people were suprised about what was in the contract after they signed it!
Last week they excavated and this week the re-bar is going in, so-far so-good.
Good luck.