Hi,
I obtained a WTR visa and then immediately applied for my PR before I left the UK (was already selected from the pool as I'd submitted EOI based on the job offer I had) reusing the same medicals BEFORE they expired. The extra costs were therefore:
1) Cost of WTR visa which was 95GBP I believe
2) Second lot of postage/delivery of material which was mainly the same as for WTR anyway in my case.
The WTR got processed faster than the expected timeline for the PR application so I was out in NZ faster. That meant a bit less stress at an already less stressful time. London passed my paperwork to NZ for the purposes of the blue stickers after approval there, and it all went fine.
Kate