It is reasonably easy to measure inclination using accelerometers (such as ADXL202/210 ), and these give you the X-Y reading. (here is an example of X-Y reading http://ww1.microchip.com/downloads/en/AppNotes/00715a.pdf )
The main problem, as far as the cost is concerned, you will face with the Z-axis (orientation). There are several offers on the net, such as for example KVH100 compass, but you will be paying top dollars for these devices.
Have a look in here: **broken link removed**