Hi, and welcome back to Just Answer.
I also have Comcast and I agree, their prices for DVR/cable boxes are quite high. However, you can call and ask if they are running any 'promotions' at this time, and get a discounted price on a DVR/cable box for a limited amount of time, and then, when that period of time is up, you can call and ask for additional promotions, to try to keep your monthly fees down.
If you want to buy a separate DVR, it will act almost like a VCR and allow you, in most cases, to record only what you're watching, so it wouldn't really be worth it. However, if you do want to buy a DVR, you can find it in Best Buy or CompUSA stores, or on the web, at eBay, Amazon, and NewEgg.com.
Tivo is another option for you, but you would need to pay for the Tivo service (monthly fee) in addition to renting a cable card to access programming from Comcast, so you would have 2 fees just to use the DVR you may buy. Tivo is available at the same stores and websites I mentioned above.
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