Picking the right size can depend on how much you want the pads to absorb. I have a couple of different sizes, you can get a variety for overnight, heavy flow, med flow, or light flow.

I got my first cloth pads from Amazon because they were cheap and great as a trial run. I'm in Canada, but these are the same ones I have on Amazon.com: Link to variety pack and Overnight size

You change them like you would disposable pads, depending on your flow. They will feel damp but they absorb really well and are superior for wicking away moisture in comparison to disposables. I'd suggest paring them with period underwear or a menstrual cup if you are worried about leaks, some people wear two pairs of underwear to keep them in place. They don't have a sticky backing so it can take some getting used to. Overall they're way more comfortable than disposable pads.

A decent price to pay depends on what you're looking for. The ones on Amazon are cheap but they function well. When you want to upgrade consider if you want something made from organic materials, cotton, bamboo, hand-made off Etsy, etc. They will affect the prices.