Well, I can give you advice from 2 angles:
If you're just looking for a 40 channel AM/SSB radio that can be modified and tuned nicely, you can't go wrong with a Galaxy 949 or 959. Both are easy to modify/tuneup, can have extra channels put in, and reliable. You can pick one of these up for about 150.00-175.00 depending on where you get it from.
Another good choice is the Texas Ranger TR-696 FD1, very similar to the Galaxy 949/959 but with a 6 digit counter and a nice looking american flag faceplate. These go for about the same price as a Galaxy 949/959.
If you're after a dual final/export radio, I've been told that the SS-158EDX is a good choice, has all the bells and whistles for a good price, in the 230.00-245.00 range.
Just my two cents worth, of course.
If you decide to go the "used" route, best bet is to find yourself a Cobra 148GTL off Ebay. Look for the ones that have the mic jack on the side, not on the front. The ones that have the mic jack on the front are the new models, and for the most part are pretty crappy.
I'm sure more people will post on this, so you'll have more radios to choose from. This is all I could think of off the top of my brain at 4 AM.