At least around here, surplus attenuators are a "sub $2" sort of thing when you find them for sale.
The last time I visited the HAM swap meet around St. Louis which is hardly a hotbed of surplus electronics these days, I was happy to pick up an assortment of NOS Minicircuit SMA attenuators for $5 each.
I have a whole collection of used Tektronix BNC calibration attenuators from Ebay and they all tested good.
As far as these Chinese ones, $8 seems reasonable if you have a way to roughly verify their performance since the seller is not going to want bad feedback but I have found name brand NOS SMA attenuators on Ebay for less than that before.