The price charged reflects not just what it costs them, but the value of the work to you. If you don’t want to pay ten quid, do it yourself. You can’t do it yourself, you say? That’ll be ten quid then, mate.
Bloke comes out of his house and walks across the road to the corner shop, asks “a bottle of milk please.” Guy behind the counter says, “that’ll be £2 please.” Bloke replies “two quid? It’s only 89p at Tesco!” Shopkeeper tells him, “well, go there then.” Bloke says “I’m not trailing all the way across town for a bottle of milk, what do you take me for?” Shopkeeper replies, “fair enough. That’ll be £2 then.”
Ultimately, they’re a business, not a charity. An LBS will do a five minute freebie in order to secure repeat custom, and it works; you’ll tell all your mates, and go back there when you want a new bike. Much as you like to think so, they don’t do free work out of the goodness of their hearts. Halfords et al work to a different business model; they’re more like a supermarket, they don’t need customer loyalty because they’ve got a bloody big warehouse on a retail park that’s open all hours.