If it is expensive to repair is always a tough question to answer. If you plan on service it your self and you already have some tools and lubrication I would say No this type is as cheap as they come. This movement has been around for a long time and parts is available in masses, a quick look in the thick books reveals the different movements you could harvest parts from like the following AS models 302, 303, 311, 313, 323, 324, 328, 329, 333, 340, 342, 344, 361, 362, 365, 371, 383, 396, 473, 546, 549, 569, 585, 595, 603, 621, 629, 636, 694, 709, 714, 717, 720, 731, 775, 790, 803, 825, 915, 951.
From these I would think the AS 340 was the most popular, in the e-bay you should get some hits.
But if you plan on leaving it to a professional one soon realize why there are so many movements for sale, especially if the case were of gold they end up there. A real shame if you ask me.
If you are interested in learning watch repair this movement is a charm to work with since it has a separate escapement bridge.
The design allows you to learn how to assemble the drive train in an very good fashion without breaking the fragile pivot on the escapement wheel.
And since you describe it like it runs for a while before stopping you might be in luck and it's just dry of oil and dirty.