How good are commercial DDS IC's for low frequency applications?
100 Hz to 1 KHz really sounds like audio frequencies.  I can, and have, used audio DAC's and some opamps to generate arbitrary frequency sine waves in the 20 Hz to 20 KHz range with better than -100 dB THD+N, better than 100 dB Signal to Noise, and very good frequency accuracy (limited by the crystal/oscillator that you use).

Good quality audio DAC's run just a couple of dollars.  The highest quality DAC's are maybe US$3 in 1K qty.  So it is not that expensive.  You'll have to add some opamps to it, but those are cheap too.

You would be hard pressed to do this another way for cheaper and/or with better quality of sine wave.

You can drive the DAC from many MCU's.  I did it with an FPGA, but that's because I had an FPGA handy.  

I should also point out that @Anindo's comment about getting a cheap module to play around with is completely valid.  That module he linked to has the ADI AD9850 on it and it might also do what you want.