Why do people do this? You call yourself a cost conscious casual user. I think you should consider yourself a clueless, lazy, impatient, want it all for free user. If you truely were cost conscious you would have done some research before getting a blackberry, you would have weighed the pro's and con's of the blackberry before taking it as a primary handheld.
Your first mistake was to run down to the nearest Rogers store to purchase a handheld. You should form a relationship with a dealer, deal with the same person there, as they are all more than willing to help you solve your problems. Keeping you, the customer happy keeps the money rolling into their pockets. My dealer that I deal with consistently gets me better pricing and can answer almost any question I have.
Your second mistake was not researching what the requirements to use the full functionality of the device were. Do you really expect that any device out of the box is going to magically give you everything under the sun with no setup? Wake up for the reality check bud.
Your third mistake was to think that the blackberry works in the same fashion as a cell phone with regards to data. Again, a little bit of research (like clicking the Search button here) would have told you that the data path for a blackberry is different from a cell phone. The blackberry uses the a different APN for communicating data. Why is this you ask, because of the end to end encryption on the device. Something which is very important to most people, but taken for granted by you.
Your forth mistake was to think that mail integration is easy and compatible with every known mail system in the world. Duh. Do you think RIM sits around and observes every free webmail service so that it can be integrated into the blackberry?
Your fifth mistake was, once again, not researching setting up email. If you think the only option for you to have a BES server is a $5000 single user license, you really are as lazy as you sound. Strictly speaking BES here, a 5 user small biz version is $2200. As well, if you would do some research (did I say that word again?) you would find that setting up the desktop redirector is pretty easy and works fairly well. If you would have RTFM you would realized how easy it is to setup filters to filter the mail going to your handheld. Once again... lazy.
Your sixth mistake is expecting Rogers to be your desktop support. This is the role of an IT person, not Rogers. If you were a Bell or Telus customer you'd get the same amount of support from them. You demand excellent tech support, but you are barking up the wrong tree. If I buy a computer from any of the big box stores, are they going to troubleshoot why my web browser won't open a page? No.
You complain that you have to purchase a blackberry data plan to use the blackberry for email. Do you understand why this is? I a little bit of... (oh no, here it comes again) research would tell you that the blackberry's work a little bit differently from a cell phone. The BWC email is actually a RIM based service, and do you think this is free? Do you think this is a right for blackberry owners? Someone has to pay for this.
Humble people don't buy expensive toys and expect them to work magically. I can't believe you actually asked whether having the mail pushed to you uses up you data allocation. How do you expect the data to get to the handheld? Maybe through some kind of brainwave? Maybe you have heard the saying, "If you want to play, you have to pay" plain and simple. You want everything to work for free with no setup involved. Seriously, 1 hour of (yes...) research here would have answered every single question you asked Rogers tech support, plus taught you a heck of a lot more about the blackberry. But you the humble user were obviously too lazy to do this. Now you have a sour taste in your mouth and it's all your fault.
I would suggest in the future a cost conscious person like yourself would do some reading up before diving into something like this.