You would have to buy them used. Absolutely no reason to buy the Vaquero new and it would be fairly hard to find a new MX5. I have owned and enjoyed both but no longer have them.
If you don't mind not have multiple target ID tones, numerical target IDs and several search modes, then the Vaquero is an awesome detector. Just be ready to do quite a bit of guessing, and some knob turning. Great depth, fairly easy to set up, ground balancing takes some practice and very sensitive to small targets.
The MX5 is an awesome detector too. Quite a bit heavier than the Vaquero. All of its features are really nice. I did not like the tendency to give threshold low tones for deeper targets in its discrimination modes, its auto tracking and kind of mushy target separation/smearing. Otherwise, a great detector.
Like silverseeker 2 said, I would look elsewhere like the MX7 or Sport if you want a Whites. Nokta Makro are making some incredible detectors too and then there is the Equinox.
Jeff