Lowtower. Thats what I would recommend and what I did myself. AFAIK, the cheapest extenders are at aliexpress. Like a chinese eBay but your cash is kept in escrow until you notify them you have received the item. Probably a bit slower than buying local but I normally get my item within about 2 weeks. I normally buy off a seller offering freight free. Here is one offer for a proextender like I bought. They are others.
Here is the two way cradle such as the one I bought to adapt to a DIY velcro strap.
And here is a four way cradle like the one in the extender the Great Divider bought. Will order one myself to experiment with.
This one gives you more options such as using dual fixing methods.
I just read your thread regarding this a couple of days ago. I was looking to do this but I am rather impatient and would like to get one within a couple of days. Unfortunately, the places I’ve attempted to shop at seem to only want Paypal so I may go that route as you’ve suggested.
PE'ing since 11/1/13. It's never too late to begin!