The cost of replacement parts for a Black and Decker blender depends on the specific part and on the blender model. On ServiceNet, eReplacementParts.com and Goodman's, individual replacement parts generally sell for less than $25 as of 2015.
eReplacementParts.com lists blender parts by the model number of the blender. The prices for parts on different models is similar. For example, gaskets tend to cost around $10, and glass blender jars are usually $22 to $25.
Goodman's has a much more limited selection of Black and Decker blender parts, but the prices on this site are much cheaper. Gaskets and blender jars on Goodman's sell for around $4 and $15, respectively.
ServiceNet offers a downloadable chart of all available parts for all Black and Decker products. If the user knows exactly what part is needed, this chart may be helpful.