Will it be 15' square? 300 sq. ft. can be arranged in a multitude of ways. In order to get cost estimates, you have to have local contractors bid on the job. Costs vary widely across the country.

3x100? 17x17? 10x30? Makes a big difference.

How big of a fire pit? How big are your chairs around said fire pit?

You can look up material costs in your area for your pavers. If you are having someone build it for you, those costs are anyone's guess.