Roaming pricing comes in three basic flavors, and which one applies to you determines everything. Best case, your home plan includes roaming in the destination at no extra cost, common within certain regions and on premium plans. Middle case, your carrier sells short-term roaming passes, a daily or weekly bundle of data, calls, and texts, which make casual use affordable and are usually activated in the carrier app; for trips up to a couple of weeks with moderate use, these are genuinely convenient. Worst case, default pay-as-you-go roaming, where data is billed per megabyte at rates that can make a map session or an automatic app update painfully expensive, and even receiving calls can cost money.
I won't quote specific rates because they vary enormously by carrier and destination and change often; your carrier's website or app lists exact pricing per country, and that's the number to trust.