amazon and ebay both have just the shell for the key fob.
Fit for Toyota Prius Key Fob Cover Case Shell Replacement Keyless Entry with Blank Key 2004-2009 https://www.amazon.com/dp/B015KEW8QO/ref=cm_sw_r_apan_glt_fabc_M764H40ARCGCGNC8ZDM9?_encoding=UTF8&psc=1