Reasonably, you can only buy what you can afford. So, I would buy the best you can for what you have to spend. Less expensive fabric doesn't feel the same as fabric that costs a little bit more. Actually, you can buy some good quality quilting fabric online, on sale for $3-4 sometimes. That is fabric that originally cost $8-9 originally. In my experience, less expensive fabric can fade faster and doesn't hold up as long. That being said, if you are just starting, buying less expensive fabric for practice quilts, until you discover if you really enjoy it makes sense.
Just as 150-200 count sheets feel more like cheesecloth and 300-400 count sheets feel more luxurious and silky, so do fabrics. The more expensive ones have the threads woven closer and give a different feel.
Hope this helps. Watch out! Once the quilting bug bites, you are a goner! lol