It sometimes gets cheaper by the day when you book something like 5 days but you can't leave 3 days early. Half the time, parking for the weekend costs as much a the flights etc. you're taking.
Last time I flew out of LHR, it was cheaper for me to park at Manchester Airport and fly down.
I've got flights next month and parking is a rip off if you want to be somewhere near the airport. Still a few £ cheaper than going by train though.
Pods are pretty fast anyway. Always been a few there and I wouldn't really want someone else driving my car to be honest.