You have possibly heard the term 'Simplex' used with Velosolex. The Solex was always designed to be simple to work on. It is after all a bicycle with a small front mounted engine with a front mudguard cut out for the drive roller to engage.
Classic Moped Spares is expensive is certainly not something that can be said for the Solex machines, with tyres under £20 each and filters just a few quid, even replacing main parts is well within most budgets. 
With such simplicity the VeloSolex is a great little rewarding project and they also appear to be creeping up in value. They look so much fun I even bought one for myself, I just hope I get time to have a go on it!