Starting TTC

So I'm fairly new to TTC and I'm looking for advice. We've been basically just going with whatever happens these last 2-3 months, but now I want to really start trying. I don't know exactly when I ovulate, just a guess based on my cycle, so I figure that's a good place to start. Where do you find ovulation predictor kits for a reasonable price? Online? Any other advice for someone just starting out?