Isn't lego.com an option then?
actually if you pick a recent set with that piece in, and go to lego.com and 'lost a part', there is a chance lego will just send it to you for free. I did that for a fairly large wedge plate missing from a set I bought on ebay, expecting to pay a small amount for it, but they just posted it for free.
How expensive was Cafe Corner?
probably cost me £200, but I had a bunch of pieces already, plus I ordered inefficiently, so you can't really take that as a guide. Most of the pieces are fairly common, but the roof (dark red) is very expensive because they are rare. Either change the colour to cheaper ones, or you can buy those from lego.com for a reasonable price.