It Depends what you consider expensive, Euro Car Parts have clutch kits starting around £90 but once you apply the discount code they come down to just under £60. (It's good practice to change the slave cylinder at the same time because of the work involved in doing the same job twice!!!)
As for fitting it yourself, you have to remove the drive shafts and gearbox, but it's perfectly possible on a driveway with a bit of help. Given it's road/rally project and not a car you need for everyday transport it might be a good one to learn on?
There's lots of how to videos on youtube, not for the Puma specifically but they'll point you in the right direction and will give you an idea of the work involved.
There is a video for an FRP but it doesn't show much detail, this one for a Fiesta shows everything much better and it's being done without the use of a ramp or any special equipment.
Good luck.
https://www.youtube.com/watch?v=C8GEIu3IEeg