I did a similar route for similar money in 1991 with a Dragoman overland truck from Kathmandu to London. They used to do it regularly like a couple of times a year but don't seem to do that route anymore. The political instability was an issue - it was originally supposed to go through Yugoslavia but that was in the messy process of ceasing to exist at the time so they had to use a ferry to Italy. Also half the passengers had to fly over Iran due to the Iranians being difficult with visas. Still some problems there.