Hi..welcome along Im more knowledgeable on newer cars, but ha you checked your battery terminals ar tight? Not had this problem on a BMW but took me weeks to find out why my Megane kept cutting out...bad design, as most cars will run off the alternator once started.
I brought my 46 12 months ago for £3900 or something like that, with respray, wheel refurb, wheels, springs, services, bushes, engine rebuild, spoiler, lights the list goes on.....I have spent an additional 3k!!!! Worth it though