I've got nearly 130,000 on mine, but it is nearing a lower-engine rebuild (which I can do myself for under $200 in a single day). After that, it will be ready to roll another 100,000 miles or more.
100,000 miles is not a problem anymore for modern vehicles as long as it is maintained during that time (mine was not). There are many gas vehicles out there with 300,000 miles or more. Highway driving is significantly less wear on an engine then city driving, and where does an RV drive most of it's miles? Keep in mind, it is worse to park a vehicle for a year than to keep driving it. They are meant to be driven (oil doesnt circulate when parked) so I'd be more afraid of a 90's RV with no miles on it than one with high miles.
Obviously, getting it checked out is key... and be willing to drop a few more dollars to get it caught up on maintenance and set more aside for those rainy days.
My last though on the issue; There are more than enough other RVs being sold that do not have 100,000 miles on it. Unless that one with 100,000+ is a REAL good deal (with documented maintenance records), it is still worth looking around
