I'm loooking for simple stats like the average number of base pair differences to normal cells, average diversity between different cancer cells, etc.
Yes, there are two genome projects, which aim to identify the critical mutations (and by looking for them, they discover all the mutations in a given cancer) by sequencing DNA from the cancer cells and healthy cells from the same patient.
These are "The Cancer Genome Atlas" (TCGA) and "The Cancer Genome Project (TCGP)". Both project publish their complete data and ways to browse them. The data from the TCGP can be found in the "Catalogue of somatic mutations in cancer" (COSMIC), the data from the TCGA on their project site.