I reckon to make roughly what you've now got, sell it and make a reasonable profit you'd need to do 4 at a time and be asking £350-400 each for them . . . that does seem a lot.
On the other hand, the new one will be do-able on a 1-off-batch but be more like £650 (seems a lot but it'll be twice the size and far more intricate)
Great idea, but if you are selling them yourself, I think your selling price target needs to be £149 / £199 (I would prefer it without the tyre = cost saving), when you consider what an enthusiast would spend on furniture which reflects their hobby / what they spend on parts normally / target audience, sales area / reach etc.
However, if you removed yourself from the end-user sales and moved up the chain to wholesale, selling to a distributor, I think they could achieve the £399/499 mark. Someone spending that kind of money on furniture will want the after sales support and backup.
Another channel for you would be as 'added value' to another item. For example, I am sure a company like Snap-on would be very interested in a supply of those to give away as promotional items with their top range roller-cabs.
For example, buy a £3k roller cab, get nothing, BUT, if you bought the £4k roller cab which is slightly bigger, you also get a hub-table / rim-table / rim-job - I haven't thought of a decent name yet, but you get the idea
All in my opinion of course!