I bought two sets of elastic tethers and a set of jacklines on eBay from this seller
and they are just as nice as the expensive ones. He sells both the standard tethers and retractible elastic tethers, in both standard snap hook and the more expensive wichard hook tethers, in a range of colors, all for about half of retail. He sells both single and double line tethers, as well as jacklines, for a price thats hard to beat. I used the Buy It Now area, but they go even cheaper if you have the patience to sit through an auction.
eBay Store - Best-Bargainz: Boat Gear: Single Line Safety Elastic Tether Sailboat
And no, I'm not affiliated with this eBay seller in any way, nor do I get a kickback from endorsing his products.