Is the Search API module able to do range facets on numeric values?
commerce_search_api sounds like exactly like what you're looking for.  Be aware of the commerce >= 1.4 dependency as of this writing. 

The module includes a product display index (configurable at admin/config/search/search_api/index/product_display):


  
  Auto-generated search index that includes all product display node    types* and related product data. 
  Auto-generated facets for all node type categories and product attributes.
  


I've used the price facet filters, with and without the search_api_ranges widget, with great success.