when it comes to construction work, you can have it good, fast, or cheap. Pick two.
If you want it fast and good, it won't be cheap.
If you want it fast and cheap, it won't be good.
If you want it good and cheap, it won't be fast.
Not all bids are equal. If some guy is going to show up with a crew or professional carpenters, give you top material, and warranty his work...that bid will be different from the guy that shows up with a couple people he just picked u from Homedepot and cheap materials.
Get more than one bid, also try to learn as much about the contractor and maybe check out some of their work. See if you can get reliable client experiences from previous clients.
Sometimes its not all about the money. Sometimes you want to be sure than the company wont go out of business in a year. You want to be sure if something goes wrong 6months down the road, you can expect it to be fixed.
Sometimes the customer experience is also important.
and sometimes its all fluff. For example, My phone and your phone could be the same. But one says Apple and the other says Tracphone. One cost $1200. and the other is $100 from walmart.
Try to figure out what it would cost you to do the job yourself, if you purchased all the materials needed, maybe hired one or two skilled labors, how long it would take you and add 10-20% markup. You can probably get your job done with 10k if you self performed it. But to get someone out there to deal with your wants and demands, and back his work, pay guys and also be responsible for any mistakes, they will probably put an easy 5-7k profit on top.