Each stint will cost you in that range. 2 stints (one per race on a 2 day race weekend) will be between 800-1200.
you can read WRL rules (
www.racewrl.com) to know the equipment requirements. In short: SA rated helmet, multi layer suit or single layer with nomex undies, gloves, shoes, socks, and I highly recommend HNR - Hans device or similar. WRL will require drivers to have them in 2016. You can share with teammates.
Also highly recommended and most teams will require - radio helmet kit, mic and earbuds in your helmet to communicate with pits. Also a cool shirt if the weather is hot.
You can find open seat postings in the forums of any of the series'. HPDE experience should be all that you need, but understand you may have to rent with a slower team to start out, most of the top teams will want friends or someone with significant racing experience.
If you guys are serious and want more detail or help with any of the above, I'd be more than happy to help. Also Paul Johansen and Shane@DB also have been racing a lot and can offer advice.