It all depends if it has structural rust or not...
The OP is looking at a truck with 102K miles.... That's a long way from a truck with 160K or 200K miles. At 15k miles per year (avg) he's got 4 - 6 years of driving before its at an equivalent amount of overall wear and tear....
If the OP buys a "rust free" truck with those sort of miles on it, he will be pushing 300K on the odometer after that same time period, and guess what? That truck that used to be rust free will end up rusty anyway. The end-result is the same, why pay a premium for a rust-free example?
That's not to say the OP should be cavalier about rust.... If the truck is basically solid, it still makes sense to deal with any bad rusty spots IMMEDIATELY to slow the creep of future rust.... Rust inhibitors, or rust encapsulators are better than doing nothing. Getting into a habit of doing yearly oil undercoating treatments will help a lot too. Most New England mechanics would prefer to work on an oily undercarriage, than one that's completely rusty so that every bolt must be torched-out to do repairs.
To be clear, this advice is for buying a "year round" driver in New England (or any other salty region). If you want a truck to enjoy only in nice weather, then absolutely seek out the cleanest and most rust-free one you can afford!
-G