While browsing the Secorbus pages (knowing no Spanish a bit of an adventure!), I did not find any links from Sevilla to Jerez and Cádiz. Is it really that they do not operate that service (the closest one goes from Madrid to Jerez but passes Sevilla ) Any suggestions on companies serving this trip? I would be looking for costs and schedules, also times of getting from one place to another.
Thank you all!

Palice

Socibus/Secorbus is a 'long haul' bus line that serves Jerez and Cadiz from Madrid AND Sevilla from Madrid. When I took their overnighter last June, they served both routes with a single Motorcoach (It wasn't crowded). Local Bus lines serve Cadiz and Jerez from Sevilla - not Plaza de Armas - the other Bus Station. I don't remember the name of the bus company (Comes or something like that). You can also get regional rail between Sevilla (Santa Justa) and either of those destinations.

Thank you Eddie. I guess the best way will be to rush into the tourist info office once we arrive in Sevilla and get all the info there as I am sure these companies would hardly have a web site. It looks like we are taking the AVE train from Madrid to Sevilla (being veeeery short of time, so will have to spare those extra money on it - unfortunately buses cannot compare those 2,5 hours on over 500 kilometres), so we would like to take bus this time. I still don´t have the right idea of local transportation but after reading the posts on comparing the service in Spain and US I guess it is not bad at all! Will see.. Thank you yet again.

Palice

There is bus/coach service between Sevilla and Cadiz - sorry, but I can't remember the name of the bus company. Its, perhaps, a three hour ride - inexpensive and comfortable. Cadiz - Jerez is also linked by bus.

For short distances there is no big difference between buses and trains in Spain. I took the Sevilla - Cadiz train last December and it was quite good. Remember to take the "Andalucía Express" because there are a few others than are slower and worse quality.

Check out Renfe website for more information.