I have just seen this post, on Facebook, from Gutsibits. It may be of interest to some here, in which case, I guess you should get in touch with Gutsibits themselves.
“Question for our customers we need your feedback, we have around 30-40 small twin gearboxes,v35 v50 v65 etc and we have a supplier who will refurbish these cost would be around £400 to the customer for a fully refurbished gearbox inside and out would anyone be interested in these please let us know in the comments”
nice idea but local engineering firm near me charges 150 ex vat for a car gearbox rebuild with new bearings and seals. £400 for a bike gearbox seems a bit steep.
don’t tell ME!!
well i can’t tell anyone on Facebook, i don’t use it 
You could tell Gutsibits! 
I think they will want to price their gearboxes at what people are willing to pay, with a markup over the recon costs, but I’m not a v35/v50/v65 owner so I’m not going to haggle with them.
OTOH if you don’t already have a gearbox to take and get reconditioned you have to add the cost in for buying one, idk what they go for now but I’ve got car gearboxes from scrapyards for 30 to 50 quid. was a long time ago so I’d probably have to pay a bit more now.