Cheapest way to get a Roamio Basic w/ Lifetime?

I currently have a TiVo series 2 w/ lifetime (I bought it on eBay and had the lifetime transferred to me.) I want to buy a Roamio Basic w/ lifetime but can't figure out the cheapest method. On Tivo's website it looks like it would be $599.99 (includes $100 multi-service discount.) The TiVo itself is $50 cheaper on bestbuy.com, so maybe I could buy it there then activate lifetime on Tivo's site for the discounted $399.99 for a total of $550, but can it get any cheaper than that? Thanks for your help