Hi UK. If I understand correctly, the 2.5k is just for re-routing pipework?
I assume this does not include fitting the appliances?
One could do a lot of re-routing for 2.5k ;o)
In which case, it does sound like a classic case of them not really wanting the job. It's not uncommon for a tradesman to price this way when he is very busy.
The thinking is that if you do go for it, it'll be a real "earner."
I would suggest that you and your husband take as long as you like, and do the maximum amount of the work that you can.
From previous conversations with you, I'd say you were both quite capable of it.
Given a few simple skills, work of this type is mostly just attitude and common sense. It'll just take you a lot longer, that's all.
If you install the bathroom appliances, then you can always call on a plumber and electrician to finally connect you up. At least you'll be in control.