Firstly, according to Michelin.com, Vale de Lobo - Granada is a distance of 466km with a transit time for approx 5hrs.
I can vouch for this as I did Lagos - Granada by car myself this time last year.
I therefore find it very unlikely that you will find a Portuguese taxi driver willing to do such a long trip.
As an example of fares, a taxi from Faro Airport to Lisbon, a distance of 280 kms, is officaily quoted in the Faro Airport Guide 2007 at up to € 317.00 for a 4 seater taxi. A taxi to Seville in the same guide is quoted at up to € 206.00. This is slightly cheaper pro-rata as there are no tolls on this route.
On this basis if you were able to find a taxi to take you, you would probably be looking at a fare of between € 430 and € 500 depending on whether week-end/weekday/day/night.
