Ted,
A lot of my oil & gas customers are buying ones from Dakota Ultrasonics. They have a bunch of models and the ones I have seen have aluminum cases, a nice display, take AA batteries (a must for field jobs) and have a long warranty. Prices start around $1000. Depending on the size of the area you are scanning, you might consider one with high speed scanning.
http://www.dakotainst.com/index.htmlTry to squeeze a case into the budget too. I like the ones made for pistols, and sold at all sporting goods stores. They have the pick-out foam and will keep dust and moisture out. Get one big enough for some couplant and spare batteries.
~thirdeye~