Tinytoes, While I was just making the tea I came up with something positive you can do that might save you a lot of money, aggro and hassle in the long run.
Dp is a builder. Whenever people call him round for quotes etc he always says 'do you have planning permission' 'no, we wanted to know how much it would cost first'
He doesn't quote before someone has pp because it can take several nights to work out a quote for some work.
He tells people (and So does Sarah Beeny on Property Ladder) to have an informal chat with a planning officer first. You get them to the site, they have a look at the property, listen to what you want to do, then give a fair assessment (based on their long expereience of types of application on various types of properties in the borough they work in) as to whether you will even get pp at all. Or if you will get it, an idea of any restrictions etc.
You state earlier that its a rare example of a cruck framed house. You also say that you wish to put a window where a door was and put a different type of door on. On a grade II listed building (and I used to live in one with dp1 who was an architect) you will be soooo unlikely to be able to make these changes. And if I haven't listed the exact changes you may have stated then don't pick me up on it as I haven't time to re-read it all to find that post).
You also think that the passage isn't a part somehow of what the listed building consent might cover when it is in the middle of and integral to, two buildings subject to listed building consent.
yes you have to give reasons for your application but I doubt very much that 'because we had child and want to move our kitchen downstairs' is not enough to change the structure of a grade II listed building.
So I'm not going to say again that your budget is ridiculously low, that if I was your neighbour I would object to someone unskilled (yes I am speaking about your dp as a course in plastering isn't the same as a long time learning the skill as a tradesman) working on MY external wall.
Please please just go and have an informal chat with a planning officer. You should have done that at the start, because if planning will not be granted then you have done all this and caused all this hassle, for nothing.