The Nidd is a good trout and grayling river although being in the most part tree lined you really need to be in the river and be using a short rod.
Starting at the head of the river you have Nidderdale Anglers (
http://www.nidderdaleac.co.uk/) who have most of the water down to Low Laithes and also Scar House reservoir. You therefore get stillwater fishing as well as river fishing. Course fishing is allowed on certain sretches and they have quite a few 'holiday anglers' during the caravan season. Certainly within your budget.
Harrogate Fly Fishers (
http://www.harrogateflyfishers.co.uk/) have the next three miles down from Dacre to between Darley and Birstwith. Pretigious club, well stocked, I think membership is around £220 + joining fee.
Locals in the 'Birstwith Anglers' then have the River down to Hampswaite Bridge.
From Hampswaite Bridge to Killinghall Bridge 'Knaresborough Anglers' (my club) have the fishing plus also a trout lake just outside Knareborough and another small section of the Nidd near Wetherby. Again, you get the benefit of stillwater as well as river fishing. The river and lake are both well stocked and managed Fees similar to Harrogate Flyfishers. The Nidd starts to become more of a mixed fishery after that point.
Fewston and Swinsty are both good day ticket waters if stillwater is your main thing.
Drop me a pm and I'll arrange for you to visit the Knaresborough Anglers stretch if you like.
Regards
Nidd