Testing a New developped website for errors and user experience

Hello,
After 3 months of work, my webdevelopper finished the design and development of my site.
Before going live online, i am looking for someone who could review the new design before i do my final payment to the developper. i need mainly to test all the functionalities making sure no bugs or errors are still existing, and no wrong functions. as well as some feedback on user experience and feels. with some suggestions of enhancement if needed
is this something you can do or interested in ?
if yes, how much would that be ?
regards