I am looking for a meta-search engine that is easily added to a
website and is completely customizable.  For example- If I had a shoe
review site and wanted my users to be able to search every e-commerce
site out there which sells shoes (ie zappos, amazon.com, etc.)- I
would input the sites which users of my site would be searching- and
only those sites would be searched.

Results would be clear and in a nice format- no extra opening of
window pop-ups, etc.

Ideally a free engine, but anything relatively inexpensive is alright
as well.  I am not looking to spend hundreds of $$$, but quality of
results are important too.

Remember, this would only search sites that I input- and return the
results from each site in a nice formatted page.