Often when visiting Lisbon with limited time, a private tour guide can be very helpful. You can be escorted by your tour guide, picked up directly at your hotel, and be transported through the day in the comfort of a luxury car, instead jumping through crowded buses, wasting hours of your limited time.
Our recommendation could only go to Sintra Magik Private Tours ,who offers private guided tours with luxury transportation and private guide (English Speaking), in Lisbon and most cities around (Sintra, Fatima, Obidos, Evora, etc).
The prices vary depending on the itinerary and the number of persons, but are as low as 145EUR for half-day PP.
On any other european capital, this kind of service would cost at least 500EUR/600EUR.