Amazon offers Prime members the Dolica Professional Heavy Duty Tripod Dolly, model no. LT-D100, for $24.99 with free shipping. (Non-members can spend $35 to bag free shipping; otherwise, it adds $9.42.) That's the lowest total price we could find by $15. It features adjustable leg mounts, wheel locks, and a black nylon case.
Update: Note that this item is temporarily out of stock, but can still be ordered for delivery when available.