New DC14 motors are £20-£35 depending on where you source them, and not too tricky to fit. Much cheaper (and better) than a new Vax. A new Dyson will carry a 5 year warranty-subject to proper maintenance.
The post motor filter is for the lifetime of the motor, if you accept Dyson's approach. The instruction manual makes it quite clear that the filter can be accessed and cleaned or replaced.
If you decide not to replace the motor, your Dyson will fetch up to £20 on ebay or Gumtree for spares or repair, if otherwise in good condition.