My mother has been a long time Bell subscriber, and a couple of Christmases back I paid $600 to get her a 9200 series HD PVR. Back then Bell was offering *new* customers a $300 credit if they bought that same receiver, so I called Bell and bitched that they were treating new customers better than their long time customers. It didn't take too much talking on the phone to get someone to agree to offer a credit. In the end, that turned out to be a *huge* hassle because they didn't apply it properly, and I had to call back too many times to get it done right... but after all was said and done, I did get about $300 worth of credits applied to my mom's account.
So, the first question is: how do you feel about getting tied back into another 2 year commitment to Bell. If you're okay with that, you could always go the route of disconnecting and then buying the new receiver as a "new" customer... (I'm not sure, but I don't think they have disconnect fees if you're outside your contract, but you'd need to check the fine print of your agreement to be sure.) In any case, I suspect if you just call and threaten to disconnect, that they'll clue into the fact that its in their best interests to not let you disconnect and they'll do a deal. Make sure you get the employee number of the person you speak with, and keep a clear record of what was promised to you, because no doubt you WILL need to call back to make them keep their word. (For example, I was promised: free HD channels for a year ($120), free professional installation ($75), a Visa gift card ($100) and one months free service $(60).)
The other option, is to switch to monthly rental... and for $20/month they'll send you a PVR, and even hook it up. I think they expect a 2 year minimum commitment on their rentals.
About doing the upgrade yourself... just remember that it is not always as straightforward as just installing a different head (LNB) on the arm of the dish... you'll need to run the new wires from the LNB into the basement, and it probably also needs a switch in the basement and your PVR will require a second cable run to it from the switch (it has dual tuners, so it needs two input cables.)
In the end, you'd have 4 wires from the outside running into the switch... that's for the horizontal and vertical polarized signals from each of the two satellites... then from the switch you'll need a wire to each receiver and two wires to any receiver that has a dual tuner. *AND* if you have enough receivers that you need more than 4 wires out of the switch, then you need a funky arrangement with multiple switches or a higher end switch that supports more than 4 outputs.
I'm sure you can do all that wiring yourself, but just make sure you have all the equipment... the switch being the most likely part you may not already have in your existing system.