Budget is likely to be the one thing that you have little control over and
will ultimately be a deciding factor on which bike you will purchase.
To get a good bike, it is not always necessary to spend a great deal of
money. I would recommend that you stay away from the discount stores if you are
a serious cyclist or hope to become one. Finding a good bicycle shops in your
area is a good place to start, although there always good deals to be had both
online and mail order. Don't overlook good high quality used bikes either as
occasionally you can get a lot of bike for your money. Just remember to do your
homework. Make sure that you examine a used bike carefully or have a trusted
mechanic check it out for you. Also, provided it is a good fit as is, take it
out for as long of a ride as the current owner will allow.
In general, I don't recommend that you skimp on components with the thought
of upgrading them later. What generally happens is that after you have upgraded
all of the components, you will probably decide that you also need a better
frame as well. Buy what you can afford, only changing those components necessary
to provide the best fit. Later, if you decide that you just have to have a
better bike, upgrade the whole thing at once. You will be money ahead in the
long run.