Looking for a shoe extension, like this: http://www.bhphotovideo.com/c/product/407098-REG/Rycote_037303.html, but that's less expensive. Or is $30 what I should expect?

I had this problem recently. I ended up getting the 10cm Rycote extender. Prices vary, but often the cheaper online stores make it up on the shipping costs. I ended up paying £24 with shipping and tax for an item listed at £15.

The Rycote accessories are well designed and manufactured, and can often be used quite flexibly - for instance by unscrewing the extender bar and captive nut, you have a hotshoe to 3/8 adaptor.