$2000 per receiver from Omnistar to RTK,  a used Trimble 750 base can be bought for $4-5000, so 3 bases = $15000. Then you own them.

You can find the new 542? bases used for $9000 or less, they move easy IF you are working close (4-5 mile of each other) you can "fence post" it in different locations & get by with 1 base. You can do this with the older bases as well by saving "bases".     I do this sometimes when I get too far by finding a good tie in a fence line & using a 5/8 bolt welded to a LAG screw that I screw into a post for a repeatable base.