Walmart offers The First Years 3-In-1 Potty System in Mickey Mouse for $17.97. (For Prime members, Amazon offers it for the same price.) Opt for in-store pickup to avoid the $4.97 shipping charge. That's the lowest price we could find by $8. It can be configured as a stand-alone potty, detachable toilet seat, or step stool.
Prefer your Mickey to be accompanied by Minnie? Amazon offers it to Prime members in Minnie & Mickey for $17.99 with free shipping. (Non-members can spend $35 or more to avoid an $8.95 shipping fee.) That's also an $8 price low.