Dover to Heathrow Transport

Has anyone used Silver Fleet or some other transport company for Dover to Heathrow? They advertise their shuttle costs approx. $90 one way. Oceania's transfer is $288/per person Dover to Heathrow. We disembark Oceania a.m. July 24. As our (Heathrow) Delta flight leaves at 9:40 a.m., we decided to spend the night of the 24th at Comfort Hotel Heathrow (actually in Hayes, a short bus drive away). Lots of mixed reviews of the hotel, but we don't feel like spending $$$$ for one night. In any event, from the airport, we'll take the Hoppa bus which costs approx $12 round trip to/from hotel. Alternatively, would love to hire a driver/guide to see the sights, if any, between Dover and the hotel. We already visited Dover Castle in the '90s (well worth a visit). Any suggestions?