You can have a price filed and order entries by price or/and use the jReviews range module to narrow down the results by price. See here:

http://demo.reviewsforjoomla.com/reviews/Amazon_Store/Digital_Cameras/

There's a sort by Lowest Price at the top of the list and a Filter by Price on the left side.

Please login to the admin of the demo and play with it, you will see all the types of fields and how the price was defined in this case.

http://demo.reviewsforjoomla.com/administrator/

There's an advanced search module which you can use to search:

Or you can use the default advanced search form

Then you need to use an integer field.

Starting with RC3 you can, but you will need to overwrite a couple of files from the frontend:

jreviews.php
jreviews.plugin.php

Of course if you want to modify the code of any of the other php files, you will have to overwrite those as well since the trial version ones are encoded.