quick one - how much does it cost to buy keywords on google?

There's no fixed price. It's an auction, so you set a budget and bid, and what you actually pay per click depends on how many others want that keyword. Some niches it's pennies, legal and insurance terms can run to tens of dollars a click. Keyword Planner inside Google Ads gives you estimated bid ranges for your keywords before you spend anything. Start small, see the real cost for a couple of weeks, then scale.