Chainring: cheap vs expensive
You get what you pay for. Cost is going to be dependent on materials, engineering, etc. If you buy a cheap chain ring it may work pretty well if you don't demand a lot out of it. A more expensive chain ring will be made of better materials (will wear longer and be lighter) and be better engineered (usually an issue for shifting; not so much for a fixie).

When it comes to parts or tools I am usually dead set against buying "cheap" since you're not just paying for the materials and engineering but also the service and reputation. If you can get a decent part from a reputable place by all means go for it, but don't buy the cheapest part you can from some shady on-line guy and expect to be able to get any help when the mounting holes don't line up.