You answered your question when you included the following in your post.

"He can switch fields on Integra."  If you want something less expensive than an Integra get a Versa.  It has the same interface a your Integra.

You don't want an Edge.  The interface is different than your Integra and won't work with OnTrac3.

Also look hard at purchasing a used 6500 or 7500.  Both can be upgraded to RTK if need.  I think both might have a low cost subscription service available that is much better than WAAS.  Please check on that because I am not sure.

Good luck!!

Jay