30K for Garage conversion with small extension

AramintaLTinhat

We are looking to convert our garage (4.5m X 2.3m) into a WC/Utility and room storage of my mobility equipment and husband's model railway. The garage is attached between our house and neighbour's garage. We would like to extend the front of the garage 3m to enclose the main entrance of the house which is on the side of the house. This to give the house a proper front facing entrance. We also need to raise the flat roof of the garage and extension to the height of the neighbour's garage which is about 1.5m higher than ours. After raising floor per building regs the roof needs to be raised.

The plan is to close up the external door at back of the garage and make doorway into the conservatory (shared wall) and put in a large window which looks out on back garden. The conservatory has central heating, dwarf wall and is a proper usable room year round.
At the front of the garage we planned to take out the garage door bring forward 3m install front door (main entrance) and large window. Install small WC/laundryroom (with ventilation) at front where the sewage drain is nearest to the house (access in the driveway).
Raise the floor per building regs requirements.
We did not plan to move the gas meter but to build a cupboard around it.

We have had several estimates. Two large companies specialising in garage conversions (includes checking depth of current footings, planning for the extension at front and building regs) the quotes are coming in around £30K (no way we as retired people can bear this cost) including VAT. We have had 3 from smaller private builders (excluding planning or building regs) come in around £16K including VAT.
Wondering why there is such a difference when adding in planning and building regs. It seems to me that the larger specialist companies are charging far too much. None have provided an itemised estimate so we can compare job for job what each part costs. I really need to get this done but am so anxious.

Furts

I would avoid the "large companies specialising in garage conversions". As a broad approach I regard these as franchises, spivs, commission merchants, and sales people. It is like requesting a quote from Anglian or Everest for double glazing - if you get my drift here.

Basically you want to be in control and not these "specialist" companies. Get your own Planning, Buildings Regulations, Specification and quotes.

Yes you have quotes, but do you really know the nitty gritty of what these include, and also what they exclude?

AramintaLTinhat

That is what is bothering me. No itemised list of jobs, though everything we want done is listed, there are no prices by them. I am not in a position (healthwise) to project manage this, but I am tempted to get it done in parts. I know what order things need to be done in.

Planning for the extension. (Given it is a very small extension to the front and it will not reach the current front wall of the house this may be unneccessary.)
Get footings checked and made ready for extra weight created by adding height to walls. Remove current roof.
Add on to front.
Raise the walls.
Redo back wall blocking in door and adding large window.
Add new roof and guttering.
Install sub floor.
Install windows front and back and door in front.
Cut internal door into conservatory.
Install step down into conservatory from newly raised garage floor.
Install WC/utility, plumbing and electrics.
Finish ceiling, walls and floor and trims.
Building regs out to check midway and sign off at end of job.

I just wish I could find out how much each individual job costs, so I know we aren't getting shafted.