This chap (one or two man band really) usually has a few second-hand bits of electronics kit which are all well priced for those with smaller wallets.
I have bought a FishFinder and a VHF from him in the past with no problems at all.
www.craysidemarine.co.uk
(It's a bit strange to navigate - hover over the three buttons at the top and more appear!)
Sections of interest are Electronics (within Sales section) and Bargins (within Specials section).
Daniel