This happened to us. We had already exchanged contracts but the seller pulled out of the sale due to a domestic dispute. Our solicitor charged us €250 euros. Which I thought was fair enough seeing as she'd done the bulk of the work. Her original price was going to be a flat fee of €1000 euro, less land registry fees etc, etc..
So ask your solicitor how much they will charge. If you agree to go back to them when you find another house, what they charge now may not be huge.
Go with your gut instinct about this sale, rather than basing on the decision to stick with this house because you can't afford another solicitor's fee. Also, if your budget is so tight that another few hundred on solicitor's fees is going to push you to the edge, it sounds like you might be better off leaving this one and trying to find something a bit cheaper.