Day trip by taxi - Granada to Nerja

It will be expensive and will take a few hours, so yes, prior arrangement seems required.
But my question is: why? Do you have someone to visit in Nerja? Otherwise it is entirely skippable in my opinion! There are better caves in America, and better seaside resorts in Spain.

I also question the expenditure of your most valuable vacation asset, time, on Nerja. Been there and wish I had not spent time on that.

I guess that makes 3 votes for not worth the effort. 😀
I spent a week on the outskirts of Nerja with RoadScholar. The cave was mildly interesting, the town okay, We did day trips to interesting spots.

Thanks - I'm under the impression it's a worthwhile resort town, and the rest of our trip to Spain is being spent inland.

According to Rome2rio BlaBlaCar.es can take you.

The way I'd look at it, is: "worthwhile...compared to what alternative?"

Choosing travel itineraries and destinations is all about trade-offs. There's more stuff to see and do than there is time to do it. So you have to pick and choose, and prioritize...unless you have unlimited time on your trip, and you will already have gone everyplace you wanted to, and will already have spent all the time you needed in all those places. I don't think that describes most vacations. In most, each day is precious, and to be spent wisely.

The critical bit that's often overlooked is touched on above by Marbleskies:

I also question the expenditure of your most valuable vacation asset, time, on Nerja.
Been there and wish I had not spent time on that.

For most of us, usable time is by far the most valuable and the most constrained commodity we have to spend.

Of course, it's your trip, and only you can (and should) decide how to allocate your time, based on your own priorities -- we've all got our own tastes. But, another way to look at it is, what else could you spend that day on? Is there something else you would enjoy more or find more meaningful? That depends on your own preferences, but also what else you have managed to put into your trip. Maybe one more day in Seville, or a stop in one of the White Hill Towns, or some place you had to cut due to limited time.

I have not been to Nerja, but I've never seen it described as a particularly special place not to be missed. Before spending a day there, I'd just look around at other places on/along/around your trip that might be a better way to spend that day.

Unless its operating model has changed, BlaBlaCars is no more than a clearinghouse for arranging to ride with someone who happens to be going where you want to go--an organized form or hitchhiking or one-time carpooling.