Phil, If you have a high enough monthly plan with Directv, the Tivo service is free. However, you technically do not have to ever "use" tivo. But I guarantee that you will. At minimum, you will have it record your favorite few shows. But the other great thing is being able to pause and rewind live TV.
BTW, I also have the Sony HD-200 (1 model before the 300), which is an excellent unit and was almost $800 when new 4 years ago. It has faster menus and a much better channel layout guide than the HR10-250, but no TIVO or DVR service. If money is a concern and you really dont want TVIO, I am sure you could find one of these off ebay for cheap.
I did buy a 2nd hard drive from weekknees. They are a very reliable company and the kits they sell are 100% perfect. They also on their site talk about the DirecTV branded DVR service and discuss the pros and cons. Right now, DirecTV TIVO is the way to go but in the next 2 years, DirecTV will stop selling TIVO and only offer their inhouse DVR Service.