The 4 Runners are truly awesome vehicles, they have one possible Achilles heel to be aware of however, the frames had some problems with rust. Some were not dipped correctly, some were replaced under recall or warranty, but many older ones that have lived in states that use aslt on the roads can have problems. Lay down and look at it from underneath, and see what it looks like. Google "toyota 4runner frame rust" and look at pictures to see what the ugly ones look like, I saw a number of ugly ones in the midwest. I found one that lived most of its life in texas, the frame was excellent. For an 05, it was in very good shape overall. I bought it at 175K, its now at 225K, with only tires, brake pads and an alternator needing attention in that time.
I believe you can drill drain holes in the frame to lessen the problem of them rusting. The issue is they are a box frame (enclosed), not a C channel frame with an open side, so they collect water, salt and crud through the holes in the sides and it collects and holds moisture and rusts, sometimes through the frame to structural failure. Its likely any box frame can have that happen, but Toyota is the one that got the attention.
The comment about replacement parts is valid in most cases, non-factory replacement parts are often lower quality, and, you generally get what you pay for. If you look for the cheapest parts, you will probably get the cheapest parts. Also, rebuilt are often more problematic than new replacement parts. I dont recall what the issue was with my original alternator, I bought a new replacement one from an Oreilys and was back on the road during a trip, but kept the original one and will look at it and see if it just needs simple parts replaced, like bearings and brushes. Id prefer to have seen mine and rebuilt it rather than the gamble of whatever may have happened to someone elses rebuild and hope they found all the problems and used good parts.
