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What's your price range? If you have $80 to spend, you can get an embedded module from edpcompany.com like their Sonaswitch Mini-A. It gives you a 10Hz capture rate, and a psuedo-analog output with 10 bits of resolution (0 to 5V). The bad news: product + no product datasheets = 1 major headache. If you have access to the surplus market, you can probably get it for under $20.
I was looking into these ultrasonic rangers before. Old polaroid cameras used them for the autofocus. do a search for "sun 660" and you should be able to find some info on it. I picked up one from ebay for about 20 bucks...but I guess that isnt possible due to your location, and it required a microcontroller interface.
also, your +5V seems to be sagging a bit...(in your sig)