The only thing available to me is the "bond record" letter which may satisfy their needs. I know "statements" exist for other ns&I products but I never saw one for premium bonds. As for registering for the adviser online service I imagine that won't be straightforward.
Does your friend actually meet the requirements to obtain a new extension? Retirement? There is nothing to be done with the e-visa system relating to an extension.
The app? I have K biz and can use it on my laptop, tablet and phone via a browser but when I tried with the actual app I got the foreigner cannot message.
I think it's equivalent of THB 500k for 3 months. Only from what I've read. (Edit: I just checked the embassy website and the amount is correct though no mention how long it should be there)
I had very good experience with WellMed Bangkok Clinic, on Sukhumvit close to soi 25. Not for PSA but for a non standard cancer test. Great service, no doctor involved. Contact them and tell them what you need, I'm sure they'll sort you out.
Of course it can be cheaper. UK passport applications need to submitted in person and collected in person. So it all depends where someone lives, nothing to do with laziness.