We're visiting Madrid this weekend and need car parking. We'd prefer to drop the car off and travel by Metro. The hotel car park fees are very steep! There doesn't seem to be a park-and-ride equivalent.
Anyone who lives in Madrid got any ideas pls?

Well, I'm not sure that people in Madrid would have a better idea, as their preferred parking option may not be convenient for you - they may well not have a car anyway - I didn't when I worked there. Of course there is the option of searching for "aparcamientos Madrid" on Google.
I personally would park the car in somewhere like Pozuelo (to the West) or Alcala de Henares to the East, and get the cercancias local train into the centre. Or, if you're fine driving into Madrid, park in the north of the city near LaComa or Penagrande stations on Line 7 - note, probably best not to park near Pitis station, as there was a community of druggies/homeless who lived there (I don't know if that is still the case). But if you're not happy parking on the street, then I suppose you'll be better looking at the aparcamientos.

Drive up to the Metro Stop in Barajas there's free street parking there opposite burger king, lot's of people park up there and go to the airport or head off into town. If you don't find any parking there, head down to the Ibis Barajas, loads of free parking there. You can either pick up a bus into town from there or 10min walk back to the Barajas Metro Station.

many thanks
We had to pay 75 euros in the end. But this wasn't the most potentially expensive part of the weekend. When a second crown dropped out and I found I had an infected tooth it turned into a presupuesto for nearly 3 thousand euros. Well, I suppose that's a trip down to my doctor a free extraction, and one step closer to false teeth. Off to find discussions on this subject

Ouch! Having had another tooth out last week I feel your pain.