Possible to appeal costs?

My partner is the respondent in a divorce (an agreed separation) and as he was initially under the impression that his stbx was in financial dire straits, he agreed to pay costs upto £1000. This was put in a solicitors letter to her. At the Nisi stage, he was aked if he had any objection to paying costs but, as he had already agreed to do so (and as we believed that these would be approx £340), he made no objection.
We have had a letter this morning from her sols requesting costs of £1140 (convenienty just over £1000, plus VAT). Apart from the fact that we are shocked at how much this is, the agreement was made to pay her costs as they had a verbal agreement to sortout finances between themselves. She has refused to talk to him about finances for several months now and we are racking up huge costs in sols bills. We are also surprised that of the £1140, £700 will go to her sols.
We have no money left, we have no savings and she is currently refusing to release any equity from their FMH. My partner has kept his side of the bargain so far but she has not by refusing to deal with him directly and running up all these costs.
Is there anything we can do? I'm so fed-up of the constant bills, all we seem to do these days is work to pay his sols bills. I just don't know where we will find £1000+ to pay this.

There is a general court rule that the unsuccessful party will be ordered to pay the costs of the successful party in a case. Therefore with the actual divorce (not ancillary relief or children cases), unless it is agreed otherwise, when the applicant has successfully petitioned for divorce citing UB or adultery it is usual for the respondent to be ordered to pay costs.

Appealing a costs order requires a hearing incurring further costs which again the respondent will be ordered to pay if unsuccessful. Therefore it's rarely worth the respondent challenging the costs , which in grand scale of things tend not to be that much anyway.

So basically we are stuffed? £1000+ might not be that much to some people in the grand scheme of things but that, plus the sols bill this month for £750, has wiped out an entire months income for my partner. We have stuck to our side of the agreement and she hasn't but we have to keep paying the bills?
We simply don't have £1150 going spare to pay this with.

You could write the sols a polite letter explaining your financial situation and offering to pay £20 a month or so. They might jump up and down but there's not a lot they can do about it I think.