I just bought a lovely purple apple snail for £3.50 in Maidenhead Aquatics.
You got a very good price there then, well done It's not often you see the rarer coloured apples for less than £7.00 for a good quality one, even from the big companies, never mind individuals like me.
Maidenhead do offer good prices on many of their livestock. They also have the benefit of being a big chain so they can vary their prices from 'batch to batch' and location to location.
Perhaps if you mentinoned your location Marieukxx,(or at least the location of the store you went to) it might be useful as not all of their stores carry the same stock, and I'm not 100% sure that they offer mail order.