Hi Alex,
I don't have and SDM in the 18" to 22" range, but I can vouch for their quality and craftsmanship.
Yes, they are pricey , but you are paying for quality here.
Peter's a top bloke to deal with and very approachable.
Word of advice..... Peter's prices are dependant on the US$, so if your serious considering purchasing one, it might be worthwhile to take it up when the AU$ is high.
Also, get it fully loaded in terms of what you want from the start. I purchased additional things down the track and even though it didn't cost me anymore, by listing what you want, its done and dusted and you don't need to worry about it later on.
Do I have any regrets ? Except for maybe not requesting a filter slide - none whatsoever!
Good Luck!
Norm