Lagos t o Jerez is only do able in two ways.
1) Car Hire.
If you are going from Lagos to Jerez and back you could pick up a hire car from one of several agents in Lagos and drive.
The route runs:
Lagos
Ayamonte (Portugal/Spain Frontier)
Seville
Jerez
Distance is: 363km
Time. (4 hours.)
If doing this run between May and September I recommend you start now later than 06:00 a.m or after 17:00 to avoid the heat of the day or hire a car with air con.
Car Hire will only be economic if you are returning the car to Lagos as one drop-off charges will be high and will only be available from the big boys like Hertz, Avis or Europcar.
Whne I hire cars to go to Spain, I usually rent from Luzcar. I took one of their Meganes from Lagos to Granada last November. There prices are slightly higher than others but include insurance for Spain and second drivers.
See:
http://www.solpraiaferias.com/carhirealgarve/index.php?option=en
2) Bus
There are twice daily buses on weekdays only year round (1st June 2007 to 30th September 2007 daily) from Lagos to Seville. From Seville you can then get another bus to Jerez.
See the following sites for info:
Cubsur's excellent site at:
www.algarvebus.info (Seville page)
The buses leave Lagos at:
06:30 Arrive Seville: 13:00
13:45 Arrive Seville: 20:15
According to this site there are at least
9 daily buses to Jerez from Seville at least two of which appeaer to connect. with the above.
http://www.seviquorum.com/transportes/autobuses/provinciales/index.htm
I suggest that you check the bus times out as the site in the Seville Forum does appear a bit old. However, I know from personal experience that there are plenty of departures from Seville to Jerez.