I use a refillable autogas cylinder ( fill it up from the garage ) costs me about £8 something per week ( on average ) depending how busy/lazy i am
Autogas is around 73p per litre.
Ive been using gas heaters for over 5 years with no problems, firstly the L5 now i use the fogwash ( it has a flue. ) where i can exhaust the gases through the roof of the van.
My heater will also heat water so hot you cant put your hand under it.
I really do think spending 3k is not worth it, hot water is hot water.
I use hot water everyday ( just because i like using it ) it wont change your life, but it does make your day to day life easier.
Its really good on first cleans & conny roof/ & gutter/ fascia cleans.
Hope this helps
Steve