Prices for multitools and swiss army knives range from a few dollars to hundreds of dollars. (UK readers can substitute pounds for dollars).
You definitely get what you pay for.
A cheap one will be ok for occasional light use but the tools will be very poor quality and won’t be tough enough for heavy or prolonged use. They could even be dangerous if you try to push them further than they are capable of. The blades and points won’t be very sharp. The metal will be soft. The engineering tolerances low. Cheap tools can also trash the things you’re working on so could be a false economy.
A quality multitool should last a lifetime so could work out cheaper over the long run. However, often you don’t need high quality tools. Or maybe you’re not sure exactly what tools you need. A cheap multitool won’t set you back much so you won’t be too out of pocket if you need to replace it.
Leatherman, SOG and Victorinox make very high quality tools and should last a lifetime if looked after and used properly. Gerber multitools are not quite so well respected as the previous brands but are good quality and provide a lifetime guarantee. You may see swiss army knives by Wenger, which is now owned by Victorinox. Wenger tools are high quality but perhaps less well-designed than Victorinox and are no longer being made.
Tools from Stanley, Draper BoyzToyz and many other lesser brands are not of the same quality and this is reflected in the price. Multitools that you see in high street department stores will generally be of low quality.
Prices vary widely depending on what tools you need so it's hard to say how much exactly you should spend, but if you want a quality multitool that works well and will last a lifetime you should go for one of the respected brands.