Abneycat

There is a point where a bicycle goes from being a liable short term throwaway to a reasonably long lifespan machine. This is the first price point you're going to hit, and it isn't that high up. When you shop around for a bicycle and pay $200 at a sporting goods store for instance, that bike may come with galvanized spokes that will seize to the spoke nipples very easily, a freewheel style hub that will be likely to develop bent or broken axles, poor bearing seals that will let things sieze up quickly, assembled by an untrained kid, it will not be likely to last a long time - you will be much more likely to encounter problems and have to replace failing parts more often.

By the time you go up in price a bit, visit a real bike shop and spend around (in my experience, in Canada) $450 and up, you're more likely to get better features. Professional assembly, stainless steel spokes, cassette instead of freewheel, double walled rims, all of these things start to show up pretty early in the "real bike" hierarchy, and make a huge difference in how long your bicycle lasts and how well it performs.

Getting quality components is the real "sweet spot", and the one that REALLY matters. Past that, you get lighter weight bikes, ones with more features, more speeds, higher tech components, and so on. Your question is quite complex and difficult to answer, because the real answer changes wildly depending on the style of bicycle that you wanted to buy. Different people are also going to give you different answers, because people have wildly varying perceptions on what acceptable components are. As a mechanic, I find anything that holds its adjustment and is designed with real functionality in mind to be quite serviceable and reasonable.

Again, my opinion is that you should avoid the lowest end. Buying parts that are designed to work, to be serviceable, and getting things which have been professionally assembled and fitted to *you* by a knowledgeable bike shop is what i'd advise.

So you know where the "sweet spot" begins on the low end, roughly. As for the higher end of your sweet spot, you should narrow down what kind of bike you want to buy, and what kinds of features you want and we can help you determine which ones offer good value in a more specific area a lot more easily.

Also, do you have everything you need for accessories? If not, you should keep those in mind in your budget. A good bicycle deserves a good lock, your brain may deserve a decent helmet (should you feel inclined to wear a helmet), and so on.