Part wall agreement at a reasonable cost??

hewhopays

I hope someone can help. We have planning permission for a single storey rear extension on our semi detached house. Our neighbours (the house connected to us) objected to our plans (although many on our street have done exactly the same thing). We dont really get on with them, although its nothing specific and we are civil.
I wrote to both sets of neighbours this week just to say we had planning and that work wouldnt start for a while but we'd keep them informed regarding when the work was likely to start and do our utmost to keep noise and disription to a minimum. I also said (to our connected neighbours) that I'd be in touch rearding the party wall agreement.
I've read a lot about the PWA and think (hope) I understand it and can issue the Party Structure Notice letter along with the Positive Acknolwdgement letter (got templates from govt booklet).
I'm almost 100% sure they will not sign and return the acceptance letter within 14 days and therfore we will be in dispute. I also think (out of sheer bloody mindedness) they will want to appoint their own surveyor - for whom we will have to pay of course.
Ive phoned a couple of surveyors and been quoted £120 - £150 PER HOUR. They recking 5-6 hrs work so thats £2k we dont have in the budget (which is tight as it is).
Is there an alternative way around this?
Does anyone know of any reasonably priced party wall surveyors who would maybe do it or a fixed fee? We're in the borders of SW London/Surrey. Thanks very much.