A little late now, but for future reference I would recommend using calculated postage if you are prepared to post bulky items, as that will automatically calculate the postage to a buyer based on their postcode when they view the listing, and making it far less likely they'll argue the cost after the fact. 

That being said, it is impossible for the buyer to "cancel the sale", as you probably know. Judging from your description of the items and so forth, the charge is fully justified and since the buyer failed to comply with your terms (contact for quote), I would open the UPI if they do not pay the invoice. One reason being that if it closes without payment, they will be unable to leave feedback (or it will be removed if they have left a neut or neg in the interim).

The only exception to that opinion / course of action would be if the listing was set up with any kind of postage cost quoted. I am presuming that it was listed as pick-up only in the postage section, with no P&H charges quoted (including 'free') and the instructions to contact if an interested buyer wanted them posted, if that is not the case that my opinion on what to do would err in favour of the buyer.