You ask two conflicting things:
"High high quality abs prints"
"Cheapest printer"
Just bear in mind that your wants are not very specific here.
Personally I am putting together a modified 3DR reprap. You can probably get all the vitamin parts and print the rest with S3 for around $400. I would recommend Hobbyking for the carbon fiber rods, Robotdigg for many of the small parts and steppers and electronics. But if you are not yet too familiar with your S3 you might not want to be working on a new printer. There aren't a lot of good kits near your $400 pricepoint. $500-600, moreso.
I agree with your idea of having a second printer as backup. Possibly, worth considering other things too, for example, my 3DR is 2.5 feet in the Z, just so I have very-tall capability in the 0.2% of the time you want it. I cant get that from my S2.
But also bear in mind the community and availability of printers is huge. I had a problem with my printer last spring before I had a second one, and posted here and someone sent me replacements, which was really nice
. (to be specific, it was Tim/Elmoret, the awesome.)