I used to drive from Lisbon-Oporto-Jerez de la Frontera quite often....and then back to Lisbon!
It's not a bad drive, but it's fine for us because we return the hire car in Portugal. If you need to go one way, from Portugal to Spain, it can get rather expensive.
I toyed with the idea of doing a one way rental from Portugal to Spain recently. For a two day rental with Europcar from Lisbon to Jerez, it was €554 as opposed to €174 for a one way to Lisbon to Faro (and then a bus to Sevilla for €16, which takes two hours from Faro). And then another cheap rental in Spain.
As I was still married at the time, and we had children with us, we didn't bother and returned to Lisbon after Jerez, so it worked out to be rather cheap as we took the rental car from Lisbon, and returned it to the same place!
I do suggest the drive though, especially if you can stop on the way. Once you have arrived in Sevilla, I would also suggest a trip to Jerez and her bodegas, and also a trip to Arcos de la Frontera - the parador there has a stunning view.....regrettably, you cannot find this view on any website, not even on the parador website. I wouldn't stay there....just eat or drink there for the view.
Also, if you like Jerez, there is a lovely hotel there which has been created in an old bodega. I won't advertise the name of it, but if you are interested, PM me. I go to Jerez very often.
Enjoy your trip!