
I guess ymmv.
I had been patiently waiting for a decent promo to come along from Excel for a couple of months. In assembling my order, I found the Excel website to be consistently the least expensive when comparing to Amazon and eBay, and that's before the 20% was applied.
The Excel website did add a shipping fee, but if you choose USPS Priority mail the rates are reasonable. On the other hand, Excel did not add sales tax to my order, whereas Amazon and eBay would have.
Bear in mind that the Amazon listing for the K18 for $3.85 is not from Amazon. That vendor charges a $3.99 shipping fee, making the total $7.84. I was unable to find a K1 on Amazon for $2.18. The cheapest listing I found was for $6.91 (with five additional blades).
The other challenge I had was there was no one Amazon or eBay vendor that listed everything I ordered directly through Excel. So, while the listing prices are lower there I would have gotten rocked on the seperate shipping fees (in addition to sales tax). I suppose if you can find everything you want from a single vendor, and are able to combine shipping fees, then you might be able to do better through Amazon or eBay.