Guy,
See my post on RTK GPS:
https://community.pix4d.com/t/4703-Discussion-on-RTK-GPS-Systems
A $2,000 RTK kit is available here:
http://tersus-gnss.myshopify.com/products/rtk-bundle-915mhz
If you have a Virtual Reference Network in your area, you may get by with 1 receiver.