.....are expensive!
A while ago I read some thoughts on cheap alternatives. Following up on this the definitive cheap solution may be cork tile infill strips and double sided self adhesive Velcro.
Stick the Velcro in 3 equidistant locations round your mute (mine is an MB) Stick Velcro to the cork strips and hey presto in less than 10 minutes you have a very good quality WT mute. That presupposes you start with a good mute in the first place!
For less than £20 (from Homebase) I was able to make 4 multifunctional WT mutes for my set of tubas!
Gaffa tape can be used instead of Velcro........ now if I'd thought of this 35 years ago I might have won a Blue Peter badge!
As and addendum I would also like to mention the quality of the Chinese tubas I bought about 2 years ago. Better than any Alex I've played, in tune, nice sound, really can't go wrong for less than £1,100 (for the set!) delivered from China.
I did have the valves redone by Roy Cox and some extensions for the lead pipes (useful dependant of the mouthpiece used and player) but they are still amazing value....even at the latest prices of about £2,400 (the Chinese realised that resellers were making a fortune!)