Can you wait until April? Ryanair's new service, between Luton and Brest commences on 1 April.
Luton Airport is easily accessible from Essex. It's a fairly short drive from most parts of the county. Alternatively, if you take a train into Liverpool Street, it's just 3 stops on the Underground (or a short taxi ride) to Farringdon, where you can pick up a frequent train to Luton Airport Parkway (which has a fre shuttle bus service to the airport). Yet another alternative route is to travel to Stansted airport and then board a National Express coach (which links the two airports with 27 journeys per day).
Ryanair are currently quoting fares of �0.01 per way, for the random dates I've tried in April. With taxes and charges, if you book before midnight Thursday, you'll get a total fare (including taxes and charges) of �5 outbound and �10 inbound. i.e.
�15 return, including t&c
http://www.ryanair.com/site/EN/
You could probably get your friends to collect you from Brest airport but, if you need travel details here they are:
From Brest airport, you can take the bus service to Brest rail station (�4.60 single, �8.40 return) or take a taxi (�15 daytime fare, �20 night fare).
Trains from Brest to Chateaulin Embranchement are infrequent bu take just 45 to 50 minutes. The single fare quoted on SNCF's UK website is �9:
http://www.sncf.co.uk/
Chris