I hate to be first, but I just happened to log on and find this, so here goes:
The common wisdom is to start with the source and work your way downstream. The further upstream in a system, the more important the quality, as what is not passed on from there can not be retrieved downstream. An opposing view is that loudspeakers vary the most in their presentation of music, so they should be selected first, according to the listeners priorities and taste. Doing so will then influence the choice of upstream components. There is no right or wrong on this subject, it is a matter of philosophy.
Then there is the opinion that the room has the biggest effect on the sound heard, so it should be made as good as possible before a system is assembled. Related to that is the notion that a loudspeaker should be chosen based on the size and shape of the listening room. Large panel speakers stuffed into unsuitably small rooms is not uncommon, I myself having done so.
Another consideration is the owners taste in music; different music's place different demands on equipment, loudspeakers in particular. A speaker great for Classical Chamber music may not be right for one who listens primarily to, say, large-scale orchestral works or Hard Rock.
Some people have a favorite amp for which they look for an appropriate speaker with which to mate it. In the same sense, the owner of a particularly favored pickup arm may look for a cartridge that will work well with that arm. Others consider this bassackwards, feeling the cartridge and speakers, being transducers, should be selected first, an arm and power amp appropriate for them then being chosen.
None of the above dictates budget allocations, and for a good reason. There is not necessarily a direct relationship between price and performance, nor between price and what any given listener likes. For instance, a panel loudspeaker lover will most likely prefer a modestly priced one to a much more expensive cone-driver speaker, for instance a Magneplanar 3.7i to a Wilson Sasha.
This is more than enough from me!