re how much it costs - probably worth ringing a few agencies and asking for a quote.
Re recommendations for your area sorry, I can't help with that one.
I would say though that the management of the agency providing the care are very important - they are a clear indicator of the values, training, attitudes of the care workers employed. You learn a lot from even the initial phone call - I have rung agencies trying to find someone to give S morning support - the responses to your initial questions are very telling.
CQC inspection/ratings are also another way to glean information..
You could also see if your local carers centre/group have a way of contacting local carers who may be able to make recommendations. You can search for Carer's groups near you here: https://www.carersuk.org/help-and-advic