Hi Cheryl,
It is hard to explain how the whole thing works, but here goes at my attempt.
If your relly has assets (including their portion of joint assets, apart from the house which is excluded if a partner is living there) of more than £23,000 (I believe that is the current sum), they will have to pay the full amount of care fees themselves. That is known as being "self-funded". You can choose any home you like, but as you rightly suggest, at £30,000 a year this swiftly wipes out any capital they have, even with their pensions and attendance allowance. Many Care Homes charge higher rates for self-funded residents, although I would suggest that with early-onset AD they may well agree to a lower rate for your relly as they are likely to be receiving it for a long period.
Once assets fall below £23,000, they are LA funded. This means that the LA pay the care home fees - but only up to a certain figure, which varies from LA to LA. In many areas this means that some homes will be charging more than the LA limit (although again, many will reduce the charges for LA-funded residents). So if your relly wishes to live in a more expensive home (especially if they have already been living there for some time) and they won't reduce the charge to the LA limit, the person has to find a friend, relative, charity etc to "top up" the fees, or move the person to a cheaper home.
That has all sorts of implications. You may not be happy to move your relative, but you also may be unable to commit yourself to years of paying the top-up fees. In my mum's area, when she entered the home in 2008 the LA limit was £375 per week, and the fees the home were charging mum were £460. Within a year, the LA limit had risen to £385 but the care home fees were then £520. You have to bear in mind that LA limits will probably only rise at the rate of inflation (currently about zero), but care home fees will rise to take account of increases in wages, national insurance, insurance generally, heating, lighting, laundry costs and food.
Also in my mum's area, there were few homes that only charged the LA rate, and all were choc-a-block full apart from one that I would not have put the dog in - and neither I, my husband nor my mum were wanting anywhere "posh", just a clean, comfortable, pleasant place to live and caring staff.
Just a correction - if the person is LA funded, it is not quite right that they pay only £100 a week and the LA pay the rest. They pay ALL of their income, whether from state pension, private pension, pension credit or savings (above £10,000 I think - they are assumed to earn £1 a week from savings for every £250 above £10,000, so if the person has £20,000 in savings the extra income is deemed to be £40 a week), less a small "personal allowance" which they are allowed to keep - which doesn't go far if they are paying for hair-dressing, toiletries, clothes, Christmas presents etc. It might be that if the person is only getting state pension plus maximum pension credit, this would work out at paying £100, but not in other cases.
Also note, if a person is LA funded they can no longer claim Attendance Allowance, though this doesn't make any difference to the person if they are LA funded.
Another possibility is to look at taking out a Care Fees Plan, whereby you pay a lump sum up front in return for a guaranteed monthly payment towards care fees. A number of insurance/investment companies provide these, but you MUST look at an advisor who is qualified to advise on long-term care plans, not a general financial adviser. However, for someone with early onset AD and no underlying physical problems, the cost of such a plan is likely to be tremendous, and also bear in mind that it might well cover, say, 75% of the care fees at today's prices, but in 10 or even 5 years' time the rise in care fees could have outstripped any rise in the amount paid out by the plan.
It can be a financial nightmare, but if you live in an area with plenty of places charging only LA rates, there is no problem once capital has fallen to £23,000. Some of us are not so lucky.
Hope this helps you to plan.
Margaret