South east England - train into London - help please.

[peppersquint]

In early May we will be travelling from France to visit relatives in the north west of England.
On the way back to France we would like to stay in a hotel (premier inn etc..) for two nights near to Dover.
We would like to commute from this hotel to London - to avoid paying higher hotel costs in the capital.
However the Ashford to London train is rather too expensive for the three of us whilst the slower train takes too long.
Therefore can someone please recommend a town/station around the south east (doesn't have to be Kent) where the travel time into central London is less than an hour and where we could park our car.
If it's within a 20 miles of Dover all the better!
Not sure if this is feasible but any tips or advice greatly appreciated.
Cheers

Luton? About 30 minutes to st pancras international on the fast train and 45 on a slower one.

I'm not sure you wil find anything cheaper on the train into central London unless you go much further in which will take as much time as the slower trainsvfrom Kent! and parking could cost anything up to £10 a day as you will be in a commuter belt. If you pick your time on the train and book ahead eg trainline.co.uk you will get the best deal (ie miss rush hour times). Trains from Folkestone take less than an hour

Does it have to be in Dover? This premier inn is on the same train line. A day return to London is £13.10 and the journey is 40 minutes. The station is within walking distance of the premier inn and it has a big car park so you can leave your car there all day for free. 10 mins from the M25 means you can get back onto the motorway network to head north really easily