I went to Walmart a while back to get a water separator for my boat motor. They had them marked down from $26 to $21. I got one but couldn't find the brass fittings for it to connect the gas lines, so I took it back and got a refund. The next time I was there they had them marked down to $6.00. I bought all they had. Five, I think, and sold them on ebay for $21.95 each.
Then I found some of the fittings like I needed and went to a different Walmart to see if they had the separators marked down. They only had one and it was $21.00 there and I watched for about a month and they didn't go down, so I bought it anyway and put it on my boat. They did have the replacement filters for it marked down to $3.00 each though and I bought enough of them to last a lifetime if I replace them once a year.