Hard to answer your question without knowing what you mean by walkie-talkie. I have a device that most people would call a walkie-talkie. I call it a handheld - for all intents and purposes it's a walkie-talkie - a hand held transceiver. I live in Rochester, NY and have talked to people in Toronto, Ontario with it - point to point when conditions are right. When conditions aren't right range still could be 20 or 30 miles - depending on the other station. Thru a repeater the range is virtually unlimited (if repeaters are linked or using internet and Echolink). It's VHF-FM and you need an amateur radio license to use it.
What you might mean by a walkie-talkie could be several things. Here in US the 27 mHz walkie-talkies were popular and they ran from 100 mW to 5 W. Many of the current FRS radios run at higher frequencies - all depends on what you purchase. A factory built radio has usually been constructed and tested with the antenna provided and has been optimized, tuned-up and otherwise developed to get the most out of it for the money. The transmitter can deliver the power to the antenna somewhat effectively, the antenna radiates power, etc. Many of the kits you see on the internet have not gone thru the development process and are more there for experimenters. In a way it's there's really not much of a comparison.