I got Price Tapestry the other day to have a play around with whilst I had a bit of spare time on my hands. I managed to create Compare Vitamin Prices Online in the space of abount 15 minutes.
Sadly as with all price comparison engines, you are forced to either edit or rely on datafeeds which to me, has always been, and will continue to be a PITA. Once merchant may call the tablets "Glucosamine yet" another merchant will call it "Glucosamine 500mg" and therefore a comparison engine will show 2 different products.
Its great for small niche comparisons such as TV's, Sat Nav systems, where there's a specific manufacturer, make and model number.
As for price, I got it last week for £75 from memory, so keep checking Price Tapestry for what seems to be daily price changes.
Don't forget PT's "Product Mapping" feature - you can configure a fixed name for a certain product and then enter all the variations used by the different merchants (conversion applied during import) - certainly manageable on [very] niche sites.
I run two websites that use Price Tapestry. The software is very well priced and you get free support plus David has several other sites and software that can be used to make the PT installation even easier to use.