Complete kit from Polly Model Engineering for a Robinson's Hot Air Engine B4 – Drawings and castings kit.  
I purchased this in 2021 for my daughter but we have not started it.  
Unbuilt but complete kit.
Purchase price in 2021 inc P&P was £165.
(Please note that the kit is supplied with pieces of brass o make the hot cap and displacer).

Video of a completed engine here:

https://www.youtube.com/watch?v=PRKb83xq6-o

Page on building the engine here:

http://steves-workshop.co.uk/robinson.html