Ok, update, and thanks for all the suggestions.
We had several people out to look but for various reasons, only had one quote: £3,000.
Like, slightly more than we were looking at paying!
It's only a few steps ffs! And they're there anyway, only looking to extend them to make them shallower and thus more accessible to folk without long legs and a ballerina's sense of balance..........Maybe I'm just out of touch, but I was expecting something under the £1,000 mark.