Well, you'll need 2 things:
1 - Batteries.
2 - A speed controller of some kind.
Sadly, because your motor is rather high voltage, you'll need a high number of cells. This rules out using any larger cells, because if if they're the right amount of energy, you won't have enough voltage.
To get to 130v, you'll need 130/4.2v = 31 cells in series.
Which means for a gokart you'll need to fit 31 of the same size of lithium battery in the hull. If you were using larger cells, this would take up too much room and weight.
The cheapest cells are used OEM EV cells, but they'll be way too big for you, and too expensive.
Since you're using a treadmill motor, I presume your budget is more like zero, or close to zero, you're hoping for a salvage solution?
Your best bet is probably to go to a tool service center (Dewalt, Makita, etc... there'll be one in every big city where the contractors go), and ask them nicely if you could leave a rubbermaid for them to put faulty lithium batteries in for you to pick up later. Tell them it's for a science project and tell them what it is maybe. They might not be allowed to, but maybe they'll bend rules for you.
Inside tool packs are 18650 cells, about the size of an highlighter cut in half. You'll get 5, 10, or 15 of those in each pack. Probably 1-3 of them will be dead in each pack, but the others should work.
It won't be too hard to get 31 of those. Or, better, 62 of them. They're capable of about 30 amps each, and you'll only need about 10-15 to power the motor at full torque.
Extra batteries added will increase range.
Speed controller can be a real hack if you have zero budget, just power resistors salvaged from stuff or that you make on your own. Not efficient, but free speed control is better than no speed control if you have no budget.
Alternatively, you might be able to get recycled lead acid batteries from an alarm or fire system service company. Those smaller batteries are usually 6 volt, and are on a replacement schedule (every 2 years, 3 years, whatever, and binned regardless of function). It would be huge and heavy, but you could use 21 of those and it would work.
It might be easier just to find and use a lower voltage motor. Motors are cheap and plentiful in scrapyards, batteries are not.