Short answer is it can't be done.
I will first assume you don't mean to actually send the WiFi signal itself over cat6 since that is almost crazy to consider.
Ethernet is limited to 100 meters so you can not use any form of standard ethernet. You could of course break it into 2 250ft segments and put a switch in the middle. Problem if this is outdoors is power and waterproofing.
You only other option is to not use ethernet. There are things called "ethernet extenders" but what they really are is a form of private DSL network. Like all dsl there will be nowhere close to the speed you can get on real ethernet. If less than 100m is ok then these device might meet your needs.
There are likely other options but since this is...