Any idea on the value of my car at PX?

[TheArchitect]

Looking to get myself a civic 2.2 i-cdti as it looks like I'm doing about 35k a year now with work. I'd like to be able to PX my MX5 in but only if I can get sensible money for it.

2006 MX5 2.0 Sport
68000miles
Good condition
Full Mazda Service History
12 months MOT
8k till next service
50% wear on all tyres

I'm not looking to sell privately as selling and buying a car in a weekend isn't really an option.

Cheers