First, the current HD programming is on the 110 sat. Normal dish 500 will receive that. CBS-HD for qualifying customers is on 148 and 61.5. The new voom channels will be at 61.5. This requires a second 19" dish.
Next, the receivers. If you want a barebones HD only cheap-o solution, buy an 811 or 6000. There are tons on ebay, or dishstore.net. For the 6000, its an older model, but generally stable. You need to buy one that has the 8PSK adaptor to view dish HD programming, and the 8VSB adaptor to view over the air HD digital programming. Also, you will need a "yellow card" with the 6000 to view dish HD programming. If the receiver comes with a "blue card" you'll need dish to send you a new card for $50. The 811 is a newer version of the 6000, but the 8PSK/8VSB modules are integrated, there is no smartcard, and it has dvi output. The software is a little bit more buggy as well.
You should be able to find a receiver for less than $200 on ebay. Not sure what new prices are.
As for the programming, the el cheapo hd only solution is to call and sub just to the HD pak. Its $10 and you get espnhd, tnthd, discoveryhd, hdnet, hdmovies. Since you arent subscribing to one of the real programming packages, they charge a $5 fee. So its really $15/mnth. If you have two receivers, they charge you $5 for the extra receiver on the account. If you want your voom channels, it looks like you'll be paying another $5 a month.
The 921 was really a "beta" receiver and has been replaced by the 942. Thats basically your choice for HD-DVR. Keep in mind anything you buy today will not be able to receive the new Mpeg4 HD channels set to debut in 2006. This is one reason why I decided NOT to plunk down $$$$ for a HD-DVR that wont get all the channels in less than a year.