Keep the price high. If you don't get it, well? You can't clean every building in St Ives!
Reasons to keep the price high:
1) If you're doing it, it's donkey work. You need some incentive to go back next time = Price!
2) If you are expanding, then you are employing someone to do it for you. Most will work slower than you, and you have to cover their money, plus make it worth your while having the headaches.
3) On a job like this you have to price high, first time at least, so you can take your time to assess how best to do it next time. You will use up a lot of time going back and forth, in and out, up and down first time around. Allow for that.
4) Not likely many others will quote for a complicated job like this nearby. They'll have to call in from further afield, so they'll be pricing in travelling time.
5) Not a straight forward job at all. Beware with this one.
"measure twice, cut once"
In short; I wouldn't take it.
Pj