I came right out of the chute saying this wouldn't be feasible on the stated budget, and I can give a little more info as to why not. It's been quite a few years since I looked into the cost of electric car batteries, so I had a fresh look.
A 24 kilowatt hour battery for a Nissan Leaf is $5500, and it's a small car with a limited range. The battery pack for the Chevy Volt, with its 238 mile range, costs over $15k, and you'd need at least 4 of them.
Batteries should fit under the floor, the whole floor, and that eliminates space for holding tanks.
That's over $60k in batteries alone, for a set of batteries that have a shelf-life. It's not like you'll be able to story mega-power to run a tiny house for decades. It's about $6000 to $7500 a year for 8 to 10 years, whether you use it or not.
You won't be able to fit enough solar on top of a bus to charge the batteries in a single day, or even 2 days, and that's several thousands more. There ARE commercially available electric buses, and they typically have their own charging station for each one.