Yes, not cheap. You can of course use your existing one but then there is no going back! In addition you need to buy the 3 1/2 pipe and get it welded - about £50. It took me about one hour to do the cutting and then grind it to a good finish. Worth the time/cost - I would say so, having seen a few other variations!
I can do the fabrication and welding myself, also have a method for ‘faux powder coating’. Might have a go over the winter.
Well done and thanks for the inspiration