One surprising fact about DVD VCR Recorders is that the prices have not come down as much as you would think, especially considering that the technology is a bit old now. Some of the units that are priced so high because of the built-in tuner. Check to see which, if any, tuners are in the unit. (The old analog TV tuners are no longer enough...federal regulations now require a digital tuner as well.) That being said, there are models without any tuners, and those DVD VCR Recorders are considerably cheaper than the models with tuners.
Another feature to look for is the presence of a true High-Definition output. While playing a VCR out through a Hi-Def line is rather pointless, you should still expect the DVD output to be HD.
You also want to pay attention to the types of inputs available on a given model. For example, some of the DVD recorders come without an S-Video input. Be sure that the connections are available for your TV tuner (cable/sat, etc.), as well as any other input devices for which you want your DVD to record.
Before you buy, be sure to actually handle the remote control to the DVD VCR Recorder. Unfortunately, many of the models out there come with rather poor-quality remotes, with tiny buttons on a non-intuitive layout. If you do not already have one, consider getting a programmable remote that is more durable, with a better design.
One of the most significant differences in various models is the media format on which it can record. The formats include: +R/-R, +RW/-RW, +R dual layer, -R, and DVD-RAM. If you want "chasing playback" (watching from the beginning while still recording), you'll want DVD-RAM. Additionally, DVD-RAM allows you to record, while watching an entirely different show already recorded on that disk. It essentially acts like a hard drive within a DVR.
Like the VCRs of old, DVD VCR Recorders offer multiple recording modes. These are essentially the modes like "LP, SP", etc., in which you trade quality for quantity or vice versa. In other words, you can record one hour of great quality, but consuming the entire disc, or as much as 11 hours of lower-quality recording. Some models offer "flexible recording length", which will increase the quality as much as possible, for a given recording, to fill the disk. Without that feature, you may be forced to choose between two settings, and if the higher-quality setting will take up too much room on the disk, the next lower mode may be a significant drop in quality.
Another feature to look for is an Electronic Programming Guide, or EPG. An EPG lets you choose a show to watch, without having to set the day, time, channel, etc., like with the old VCRs. Again, some models do not include this, which can be a hassle.
Lastly, check to see what resolution is used when recording, if you are interested in storing HD programming. Some units will down-convert the signal, so even though you are recording an HD show, the playback will not be high-def.
The bottom line when choosing a recorder is to consider what you will use it for. If you are converting old VHS tapes to a more permanent storage, you may not need the high-level resolution, and can focus on the max recording length. (Keep in mind that you cannot record commercially-produced VHS tapes to DVD, as they are encoded.) If you are looking for a DVD Player/Recorder that also happens to be able to play an old VHS when you want, you should focus on the DVD output. By matching the DVD VCR Recorder's feature set with your needs, you will be happier with your purchase.