The bicycle used to be a cheap and simple thing. The fixed or single speed bike is one of the simplest and most efficient vehicles: a machine with the minimum number of parts, all of which use well established technology. Clubmen used to commute to the factory all week, then take off their mudguards (US = fenders) and ride 10+ miles on a Sunday on steel framed, steel wheeled single speeds, or fixed, or 3 speeds.
Somewhere along the line, the bike became a fashion accessory and a money pit. People will tell you to buy an expensive one, upgrade it, take off heavy bits and add lighter bits, and then you will need to spend a fortune negating all these advantages by buying a big heavy lock because the bike has become so attractive to thieves.
You do not have to play this game. Buy a bike that feels the right size for you, because fit is important. Look after it, keep it reasonably clean, oil the chain, learn the basics of maintenance (if you don't already know how) and keep the tyres pumped up.
In due course, if you really take to it, you will start to learn what you personally would like from a better bike. Do you prefer riding on urban or suburban roads, or long rides in the countryside? Do you like to explore rough tracks and paths? Do you need to carry any luggage? Do you prefer spinning a low gear or pushing a high gear? Etc. Etc.
And then, from a position of knowledge and personal experience, either upgrade components or buy a better bike when you know what you actually want.
People will always find it easy to tell you how to spend more of your money: for only an extra week's wages, you could buy... Remember that bicycling is essentially a very simple thing and you do not have to make it complicated. Get one you feel comfortable on and enjoy riding, then ride it.
