I've seen worse. The hard part is figuring out if it's a weekend or two of elbow grease and you have something sailable, or if you're just polishing a turd. FYI, my bilge was covered in a similar layer of rusty coloured crap, but it isn't rust, I have spent the last two days cleaning it up and now I can see clean bare fibreglass. Not a hint of rust on the keelbolts or anything else in there. The Ranger looks to have a very shallow bilge with no pump so any water that did get there is just going to stay there.
Did you get any photos of the rigging (running and standing), blocks, decks etc?
It's the bits you couldn't see (sails, cushions, battery) that are going to make/break it assuming everything else is OK.
If the cushions are gone then you are going to be looking at a thousand bucks if you do the work yourself, sails are going to be probably $1500 if they are shot. Running rigging for a 26' is only going to be a few hundred as long as the hardware is all good.
Also, you don't have to go to 30ft for something with standing room, my 27' has almost as much space a lot of 30' boats with standing headroom in the saloon at least.
Anyway, sounds like the boat didn't speak to you, so go look at some more, that's the fun part of buying a boat