It depends on lots of factors TBH.
£50 might not seem that much, but what's it's real value to the customer? I think that's the question that is likely to define whether or not you'll get the sale.
Photography is fantastic, but sales is a big grey area. Prices and packages differ so much, there is no general expactation like with other things. For example, if you need a new pair of glasses, for lower end of the range designer glasses for one pair, no matter where you go, you're going to expact to pay £100-£150ish inc lenses, and with those you'll be able to see more clearly for around 2 years if you're an average person.
Photography prices change from company to company. One person may offer a mighty good deal for £70, a few prints, sitting fee etc etc. Another might not even entertain a person whose budget is less than £100.
I'd like to think that it wasn't so complicated but it is. Then people get worked up with sitting fees and all that - from the customers point of view, put it into an example...
£100 sitting fee then £10 per 10x8
The cutomer, in their eyes, is paying £100 but they don't get anything from it unless they pay more. Which is why the packages of £x for sitting and y amount of prints work.
...sorry for rambling on...