I'm not sure keeping your prices the same is a good idea. It's ok if you've only been going a few years but any more than that then past customers on low prices become less attractive and if you suddenly realise that and increase them you could lose them anyway. As opposed to new customers on current prices.
A better way is to give them a lifetime discount card, say 10%, that way you can keep your prices current but still offer a saving to your loyal customers.
Simon