Got to be worth at least a fiver - I'll give you £10!
Joking aside, have you had a look round flebay etc to see what the equivalent boat goes for?
There's a lot to take into account - certainly looks good from the pics, and that's a low mileage engine, BUT if, for example I had to drive up from deepest Cornwall I might be looking at spending less on the boat due to the distance.
You have a looked after looking boat with a couple of electonic toys - The 411 is now old hat (I believe it's in the process of being superceeded) and they weren't that expensive to buy in the first place. No idea about the garmin, but remember electronics do drop in value progressively more than, for example hulls. On the plus side it's all wired up & ready to go, and Garmin do have many fans out there.
So, I would turn it the other way - what would you expect to pay for your boat? (and take any rose coloured sunglasses off - imagine you have a wad of cash in your hand that you are about to hand over to a complete stranger) - That's probably a good going in point.
It looks like a nice boat. Luck with the sale.