I'd be a little hesitant about a Rails developer with all of the required skills in that job posting who'd take 25-40K in Cambridge. I know the economic climate isn't great but that's going to be a tricky role to fill.
Upvoted and I agree, we're offering equity (common stock) too (and have a pretty high valuation). We have four interviews lined up now for the next two weeks, it's not been easy though you're right. We ARE a startup (3 months old) though and bootstrapping still from the angel round, however, we're now in talks with a couple of VCs atm. Would be a good time to get in tbh. The job description and required skills is way too optimistic and we haven't used the one on the site for some time, I should update that to 'good developer who can learn on the job' :)
Training a competent developer across from another technology certainly seems to be popular in the UK nowadays, especially outside of London. I can't see why it wouldn't work. The equity point is interesting and does tip it in your favor somewhat.. Most of the comedy "senior" Rails developer ads offering 28K or whatever are at consultancies or agencies where the chance of any riches is extremely low ;-) Good luck!
Looks like you guys are doing very interesting work - I've been working in healthcare in the UK for more than a few years now....it's definitely wide open for some decent solutions. Are you open to remote/flexible working or is it on-site only at the moment?