The big difference is that you will be able to get a good quality fixed blade knife for much less money than a folding equivalent.
Once you are in the mid-market the practical differences are really more about personal preference.
Ease of access is a bit of a moot point, a fixed blade knife doesn't need to be opened they take up more space when sheathed so you need to find a convenient place to carry them and unless you are going for an out and out emergency rescue knife with a dedicated quick release sheath this is a debatable advantage. There is also the converse argument that if you are upside down underwater a folding knife is less likely to accidentally stab you.
In terms of durability and reliability there is less to go wrong with a decent fixed blade knife as it has no moving parts. There is also the consideration that virtually all folding knife locks can potentially fail if they get excessively dirty which is potentially dangerous.
In terms of utility folding knives are a bit compromised by the need to fold which places limits on handle and blade shape.
Another consideration is that most folding knives are made from stainless steel as he folding mechanism is inherently more vulnerable to corrosion. The choice between stainless and plain carbon steels is largely one of personal preference but in general stainless blades are harder to sharpen and so carbon steel is often preferred by people who use their knives often, although stainless has obvious advantages if you are operating around water, especially salt water.