Fewer businesses offer a fax service today than a year ago. This increased scarcity coupled with increased rent and labour costs are reason enough for newsagents to review pricing.
My suggestion is you check the pricing of your nearest major competitor and peg your price slightly above theirs. In several newsagency businesses I have discussed this with recently, they would increase their priced by a third or more. As long as volume is maintained, that is a nice bump to the bottom line.
Providing a fax service costs time and money. It needs to be price and run as a profit centre for the business.