I am thinking of parting company with this model Walkman. It is in very good condition (hardly used), has its original box/instruction manual and comes with a pair of Sony dynamic MDR-W10 headphones. There is also the external speakers for this unit (Sony SRS-7).

I am wondering what sort of price I should be asking?

That walkman will not fetch a high price. Reason being that it is based on a low end model. Original box/manual helps but don't expect much.

What sort of ballpark figure would you say 'not much' is? 

Righto, cheers for the advice- now up on that well-known auction site!