You can buy an unbranded diving watch with Seiko movement for less than £100.
There are also decent dive watches with the Miyota (citizen) 8215 movement, which is a basic reliable workhorse, for the same money. It's worth trying an established long term independent watchmaker for a service, as some of them might have parts. I was lucky enough to get a vintage Seiko chrono serviced/repaired this way.