If you are performing analog input and ouptut at the same time and the 4451 is out of your price range, you should consider looking at some of our E-Series devices as well. It will help you if you already have a couple of key specs determined, such as number of channels, sampling rate, and resolution.
Take a look at this web site to browse through some of the specs of our E-Series devices. You might find something which will still meet your requirements and is lower priced:
http://sine.ni.com/apps/we/nioc.vp?cid=10159〈=US
Jack Arnold
Application Engineer
National Instruments
