The total cost of the system depends on the selected VNA. Third-party extenders, \including VDI extenders, only work with 20GHz CMT VNAs and require one booster kit for 2-port VNAs (C4220) and two booster kits for 4-port VNAs (C4420). The extenders are packaged in small and versatile enclosures that allow for flexible port arrangements. VDI extenders can be purchased from CMT or VDI.