Apologies for the essay but you did ask :-)
It's a bit difficult to estimate because we didn't have a budget for it, we just did it as we went along, room by room and had money to do various bits. We actually started it in 2011 but then had family issues (2 sets of aged parents with health issues, both long-distance and in different towns) and then I was made redundant which slowed it all down.
We did as much of it as we could ourselves; we did all of the existing plaster removal, insulating, replastering and redecorating, all of the draught-proofing and insulating the floors and roof (we chose to replace/repair and draught-proof floorboards but insulate underneath).
We ebayed/freegled some of the insulation and battens, the rest was purchased online room by room. I learned to plaster or as it's known in our house 'vertical cake icing'!
We freegled/ebayed 3 of the windows and put them in ourselves, the rest were installed by a local supplier in 2 lots.
We purchased and fitted new front and back doors ourselves
A local installer supplied and fitted our boiler
A local builder rebuilt our old and draughty dormer and supplied and fitted a new window but we did all of the prep for him.
We bought and fitted our Tado system
We also bought and fitted a new kitchen (partially with ebayed carcasses, the rest bought new), knocked a wall down to make a room larger, de-arteced all of the ceilings and sanded 2 lots of stairs. We would have liked to build a porch at the front of the house and install solar panels but we ran out of steam and money. I now never want to see building tools ad equipment again in my life but I'm really glad we did it.
A rough back of an envelope figure would be around £5000 over 3 years, with the bulk being for the dormer, boiler and windows, although I was really happily surprised how little the windows actually cost, I'd always thought replacement windows cost mega-bucks. This includes new white goods and kitchen appliances (listed below).
We managed to defray some costs by re-selling many of the tools we bought as we went along, although I was sorry to wave goodbye to my 2015 birthday present - an air compressor and a nail gun (it was my choice, not my only present and soooo much fun :-D )
We also took the opportunity to buy a new washing machine with a 1600 spin speed, a dehumidifier for use if I can't dry outside, and to ditch the dishwasher (they seem to need replacing depressingly frequently). More recently we upgraded my old and well-loved pressure cooker and slow cooker to a multi-cooker (pressure-cooker, saute pan, rice cooker, air-fryer, slow cooker all in one), and bought a halogen hob (gob-smackingly more efficient than a standard hob), together they make quite a difference to my utility bills. We're also head-cheerleaders for merino base-layers and socks and rummaged wool blankets for snuggling into on cold winter evenings :-)