In reply to ksjs: I've vaguely been involved with hearing and it's a hidous business because although the instruments are *relatively* cheap - providing the aftercare and service necessary to make them work effectively (i.e. tune them to the user requirements, provide training on the features and keeping them clean) is EXTREMELY expensive - not least because you are dealing with - er - deaf people!
I persuaded my Dad to spend £2000 on his, I'm not sure how much benefit he got though because the aftercare wasn't as good as it might have been (mind you, he did live on top of a hill) and he was a stubborn old beggar anyway.
A number of opticians will provide hearing services, usually via a 3rd party, if you choose a good independent optician they will have their own reputation to consider and will also provide a location where your relative can physically go to have the instrument serviced, get new batteries etc.
My understanding is that it is very much a world of diminishing returns, i.e. you have to pay quite a lot more for quite a small increase in performance, but it may well be worth it.