We ended up booking our private guide through another recommendation:
www.toursforyou.pt The guide we had was named Josue (he said to call him Josh). The cost for our van (6 of us) was 270 euros and so worth it!
We spent the morning in Sintra (great town!), ate lunch at a nice restaurant there and the afternoon in Lisbon. I'd highly recommend this wonderful young man (although from what I understand all of their company guides speak perfect English). Lisbon and the surrounding area is a fantastic city to visit.
