Like probably most of you I do own at least the majority of the books in physical form. But sometimes it's just easier to read on Kindle.
Sadly they're about £5.99 each, which is absolutely worth it if you can afford it, but x41 books it really adds up.
The good news is, if you check regularly you'll find that one or two books go on sale at a time for as little as 99p. Personally I pick up anything that goes under £2, currently I think that's just Guards! Guards! but they change all the time.
If anyone knows what schedule they change on that would be useful info, atm I just have a reminder to check back every couple of weeks.
(link is to the UK page but I'm sure the same applies on other Amazon sites too)