Vidago is approximately 140km from Porto. There is no direct bus service from Porto Airport to Vidago that I am aware off.
I have made a quick simulation using the Portuguese national taxi assoication simulator. A base price for a direct taxi trip would be about +-€ 160.00. This may increase depending on time of week number of bags. Most taxis carry 4 pax and a limited number of bags. If you have a lot you may need a bigger vehicle.
You can see this here: http://scr.bi/9eM3Br
A local airport transfer service quotes in the region of € 174.00.
See http://www.low-cost-transfers.com/porto-airport/.
National long distance bus company Rede-Expressos operates two services a day from Porto Central to Vidalgo with a change at Vila Real. You would need to get a taxi from the airport to the Rede-Expressos Porto Depot.
See this document I have posted for timetable and prices.: http://scr.bi/9jXZhg
Prices are € 11.00 per adult. Bear in mind there are only two buses per day and they are each of +3hrs duration with change of bus in Vila Real..
The Rede Expresso depot in Porto is:
ROD. BEIRA LITORAL-GARAGEM ATLANTICO
RUA ALEXANDRE HERCULANO Nº366
4000 PORTO
Tel.: 222006954
See this article on my blog for map to bus station.
http://bit.ly/aJawrR
If the bus trip is not to your liking it might be as well to consider car hire. The north of Portugal is lovely - I've just been up there. You do need a car to explore.
Companies like http://www.autocarhire.net are offering 5 door economy cars for +-€ 260.00 per week at present from their Porto Base.
