For GCP's, I'm blessed with a couple of surveyors that work for my organization.
If you are patient, you could get by with a standard handheld GPS, put it on tracks mode, and then overage the tracks for a location for 30 minutes to and hour (the longer the better). You want at least 4 points, so that is a lot of patience... .
For RTK there is a wide range of options. On the less expensive side, I've heard good things about Piksi: https://www.swiftnav.com/piksi.html but don't have any experience with it myself.