Hi
First. Put a new thread out in the introducing section saying where roughly you are ,what you have and maybe few pics. Will gain favour.
With the gearbox if you have skills and place to do it source another box from one people are breaking, put it in with new clutch while you do it. If you have space
Gearbox max £100 ( but that would have to be a recent recon)
Clutch £70-£120
Simples. But it's not a job on the drive, need mate with workshop.
If you sourced a box and clutch and worth getting heavy duty clutch arm too then shouldn't be over £400 all done