Leaving the car aside a minute I too found myself in that situation of needing a new boiler a year after becoming disabled and had British Gas quote me near on £3,000 for a new boiler 10 years ago.
Before signing on the dotted line for the boiler I by chance came across a scheme going back then under the Warm Front or Warm Homes, can’t remember exact name but because I was on the then DLA the scheme gave me a grant to install a new boiler but with their contractors and two weeks later the new boiler was in.
I think that scheme finished a few years ago but worth checking if they do something similar today as long as you haven’t got ten’s of thousands in the bank you might get help.