A secondhand wheel should be around 80% the cost of a new one. Some wheels fetch more - there's a waiting list for a new one; the original maker's models fetch a premium, for instance. But there's no such issue with the Minstrel. They do come up on Ravelry now and again.
Winghams have the Minstrel at £340, carriage free, and with a £15 voucher to spend on fibre. Walnut or mahogany finish adds £30 new. So the most I'd pay for a Minstrel with 3 extra bobbins (that 6 in total is it?) is £287, or £310 with the fancy finish.
If saving money is a factor, and you don't need the extra bobbins or a fancy finish, then you're looking at £325 new (assuming the £15 fibre voucher has that value to you) vs £313 secondhand. No contest, in my view.
If you'd use the bobbins (and I'm assuming they're Kromski bobbins not one of the cheaper makes) and like the finish on the secondhand one (and I'm assuming it has one of the fancy finishes) and it's all in excellent condition, and the shipper takes the risk on shipping (which they should), well then it's being offered at a reasonable price.
If you can afford new, I'd always go for new over buying from an unknown seller and shipping from same. Buying from someone you know locally, and can collect or they can deliver, then it's worth saving the money.