There are basically two major types of generators for this situation: traditional and inverter generators. The expensive ones are the inverter generators, and the difference between the two types is the major price differentiator.
The electrical power used in residential applications, and likewise the devices you'd power in a camping situation, is alternating current, at 50hz or 60hz depending on where in the world you are. Many devices, especially motors, are somewhat sensitive to the frequency of the generated power. The frequency of the power is directly related to the speed of the engine. As a result, for a traditional generator, the ability to throttle the engine is very limited, so what ends up happening is the motor runs at full blast pretty much all the time, regardless how much of the rated output you are drawing.
In an inverter generator however, you have sophisticated electronics between the generator and the output. They are called inverters because they convert the AC of the generator into DC, then invert it back into AC. What this affords is precise control of the frequency of the output, and thus precise control over throttling of the engine. In practice this means that for a typical power rating, an inverter generator will be lighter, smaller, and quieter. Some of the nicer models you can barely tell are running if the load is low.
Inverter generators are superior in virtually every respect except price. Apart from price, traditional generators are usually a better choice for industrial or commercial applications where the generator is meant to run full blast all the time, such as construction lighting and pumping applications.
Once you are shopping limited to one style or the other, the differences in price should be sensible to infer from the specs, e.g. higher rating, trusted brand, quieter etc will all fetch higher prices.