I've used a low-end Dahua DVR as an encoder with a Vigil NVR: pulling a stream from the DVR uses the exact same RTSP:// URI as getting a stream from their cameras (just change the "channel=" parameter). Last time I actually checked the price, four-channel models can be found for around $99, which breaks down to $25/channel (not counting NVR channel licensing, of course, but that's assumed to be a constant).
The Plustek VS 540i is a 4 channel encoder with a street price of $200.
Axis M7010 is 16 channels for $1,200.00. A little more than the Bosch, but wider VMS support.
If you are willing to lock yourself into Exacq, the LC-Series NVR's are a steal. One with 16 analog inputs and 1TB of storage can be found online for $1,500.00 (cheaper yet through distribution). The IP only units (no analog inputs) are only $300 cheaper - so you are basically getting 16 channels of encoding for $300.
HikVision and Dahua brands from China, both have low-cost single-channel, four-channel & 16-ch IP encoders. Dahua's units cost around $100 mark for single & four channels while a low-end 16-ch is in sub $200 mark. Grandeye also has really inexpensive single & four-channel encoders around $100 mark.