The brightly colored neon monster of a tank that he had before just wasn't going to cut it in our home so we set out to find something else that would work instead.
We used this jar (the largest size) to make the actual aquarium. The lid was cracked and it could no longer serve it's previous kitchen-ly duties. ($15)
After placing some smooth rocks in the bottom (Betas like to lounge on things) we attached an external thermometer to the jar. This helps us keep an eye on the water since Betas aren't too keen on temperature changes outside of 2 degrees. ($2)
A filter from Walmart and made by Tetra were attached, although there are others but since this is just one fish, we didn't need a larger one. (roughly $8)
Due to Nemo's location (near a window) we also added a heater. Also made by Tetra it's fully submersible and is a workhorse at keeping his water regulated. ($7)
The plants are cuttings from a relative that love being water logged. They are super happy and super healthy. We used cotton kitchen twine and tied it around the lip of the jar to support it's stems. First we ran a length around the circumference of the jar. Next we ran it from 12-6 and 9-3 perpendicular across the top like a grid. It does great at holding the plant up out of the water without becoming all gross and icky. (free)
Nemo is happy and healthy with regular water rotation and is always asked about by visitors who want to know "where we found such a great aquarium." A little creativity and roughly $30 ($15 if you don't count the canister we already had on hand) and we became "fish people" ourselves.