What exactly is the difference between SSD Express and SATA Drives?

I was looking on Komplett this morning for SSD Drives (to paraphrase the Stereophonics “Im just looking, im not buying, yet”) and was suprised to see a big difference in price between SSD SATA drives and SSD Express Cards. they are selling a 32gb express card for about 100EUR, but  the cheapest 32gb SATA Drive is over 900EUR! am i missing something? the memory difference between the 2 should not really be all that different, and the interface should not cost nearly 800 euro, so what exactly is the difference? and, as a secondry question: if 32Gb of memory for a Express card only costs (roughly) 100euro, why cant we stick 8 of those “modules” together, getting 256gb of SSD storage (even if it is slower than the stuff in the SATA, if that is the case) and have very large, but maybe slower, storage for smaller devices?