AHRS survey:

• Low-cost INS
  They attempted to build a three-axis INS for under $500.
• MicroIMU
  Tiny (the size of a quarter) IMU / AHRS. Can be hooked to air-data sensors. GPS input. Looks great, but no prices or current draws are listed. The company rep told me that the IMU is $12k in single unit quantities or $8k in OEM quantities.
• TCM2-50VR Tilt/Bank sensor
  This is a tilt/bank/heading sensor with a 50 degree range for the pitch and roll axes and a magnetic heading sensor. It has a fairly fast sampling rate, consumes little power and is only $385 in single unit quantities. As long as the UAV does not go inverted this might work (no 3D operation). It is somewhat large for the LMH prototype, but fairly light.
• Outside only autopilot
  The FMA Direct "Co-Pilot" is the least expensive of all the options. At only $120 in single unit quantities, it is worth experimenting with. On the down side, it does not work indoors, with cloud cover or IMC, over snow or uneven terrain and only functions up to some unspecified height AGL. It also directly controls servos, so integrating into the EFIS is not easy.
• Futaba PA-2
  Similar to the FMA Co-Pilot, the PA-2 uses optical sensors to tell sky from ground. Usefull outside in good weather, but the FAQ even mentions that it does not work without a clear view of the horizon. Also claims not to work with helicopters. Low current draw (5 mA @ 5V) and cheap ($52).
• PDC-3200 Rate or Gyro based autopilot
  Expensive. Ground station library provided. Full INS + GPS + Altimeter. Unspecified power consumption.
• Crossbow technologies
  Industrial sensors. Popular for many UAV projects and used inside many of the packaged autopilots. $5,000 to $8,000 for single unit quantities, fairly deep discounts for volume purchases.
• PC Flight Systems
  $1,400 for single unit quantities. Requires rate integration to be done externally, but does have a vertical gyro. Comes with software for WinCE that acts as a full EFIS -- designed for light aircraft. Not certified for IFR operation.
• 3D Bird
  Flock-of-bird tracker for VR applications. Might work; waiting on a price quote.
• Micropilot MP-2000
  Very nice, very expensive. Ready to go for fixed wing, nearly ready for helicopters. Some what heavy and large for the prototype and not directly useably as the onboard system. It would work with a separate computer, rather than replace it.
• Buy three piezo gyros
  Roughly $50 to $100 per gyro. Lots of drift and requires external rate integration. Requires hacking to read gyro data into onboard system due to PWM output, which puts a large real-time load onto the computers. We've successfully done so, but the drift and precession rates are very bad. There are literally hundreds of models, with a wide range of features. Adjustable gain is nice, as is "heading" hold. Further details on sampling and waveforms are available.