Here's Fender Modern Player SS Jazz that sold on here recently to give you a rough idea of the price:
Don't know much about them myself but it's maybe worth sending 2x18 a message for his thoughts, although £300 sounds cheap, depending on whether or not the refin is good. The only thing I really know about the Modern Player series is that they came from the same factory as the top-end Squiers, like the Classic Vibe Range, J Mascis Jazzmaster, Matt Freeman P Bass and the Biffy Clyro sigs, so the quality should be pretty high.