My two cents for what it's worth.
As a collector with limited means there isn't much you can do to alter the situation that you painted out (if it is true to begin with). Keep in mind that even if a dealer is doing what you claim they do then that's alright because for them it's a business. If anyone else were in his place they would do the same. The guys who sell used cars do the same thing. They buy a used car for cheap and sell it at a markup. You can't really bargain with the guy unless you know everything about cars.
However, there are certain things you can do:
Firstly, decide if you want to collect just because you love stamps or because you also want your collection to have some monetary value.
Next, if you don't have deep pockets, you have to scout on
ebay for the best deals you can find. There are some pretty good deals if you look properly and there are ways to reduce your overall expenses.
Example: If you find a single stamp from a seller that you need / like. Before you buy it check if the guy has other stuff too which you could afford and need. This way you cut down big time on shipping and buy more stamps.
Try and look for deals with free shipping (Will save you good money)
To start with, buy the more common stamps that you need to fill up most of your topic. Only once the vast majority is complete will you start needing the really rare ones which will make you feel it on your pocket.
I know I strayed off topic but only trying to help.