There are many GPS receivers that would work with a laptop for field work. Almost any receiver that supports NMEA 0183 output and can be attached to a differential receiver will work for you. Costs range from about $2000 to over $10000. Less expensive receivers may work, but in that price range you get what you pay for.
With an upcoming release of Farm Site, you will have the ability to use your laptop and GPS receiver to draw field boundaries, measure the location of soil samples, and other site-specific field tasks.