You only really have 2 outlets for selling this one: domainers, or boostmagazine.co.uk
One might think if they've had the dot.co.uk for years without regging the dot.com, they aren't interested. However, companies do upgrade their extensions later in the game, they often put this off due to other priorities or to not having the cash initially (the latter case only referring to when the higher extensions are regged and are valuable).
Their company looks like it's a going concern, but not a huge biz. I'd think an end user price of 300 - 600 is realistic for what the name is and for the size of the company.
Note that all the above is moot if it turns out they actually have a trademark on 'boost magazine'. There appears to be no US tm but I don't know about Scotland. There are well over 1000 tm's for 'boost' in the US so you'd better check to make sure none of those refers to a magazine...
As for selling to a domainer, I think it's a tough sell. Pretty much no traffic name, no use for a minisite, and only one realistic end user who doesn't look like they would pay a lot for it, if anything. And I'm leery of having a name in my portfolio that might or might not be a tm problem.
At any rate, send the dot.co.uk people a short email, asking if they want to upgrade to dot.com, and you'll have your answer as to its value!
GL
