Hi Tom,
I've used all the Tesoros you mention except the Vaquero but I'll still make some suggestions.
Tesoro is unlike some companies, they don't change model names for no reason.
Tesoro has believed in constant improvements in their machines. This is why the drastic name changes.
The older machines still are very good but generally speaking the newest models are better.
I owned the original Silver Sabre but the new Silver uMax is a better machine. It's deeper and more sensitive to smaller good targets (in my opinion).
The same is true of the older ground balance machines. The Bandidos are good detectors and if you can get one in mint shape for $200, go for it. These hold their value and if you want to upgrade you'll come out good.
The old Bandido II and Vaquero are probably very close in depth. But the V is far more advanced and the better machine.
But a Bandido in no way compares in depth and performance with a Tejon (Tejon's are deeper than Vaqueros according to James Gifford). Sometimes Tejons can be had in used excellent condition for $350. People sell these cheap for the same reason people sell Minelab GT's cheap--they don't understand them.
You may be wise to buy a ground balance machine. If you have some nasty rocky areas you can ground balance the detector to certain rocks and continue to hunt the area.
Here in dust bowl Michigan the Silver uMax with 12x10 concentric coil beats or matches anything out there. Not long ago I dug a rife shell that must of been 14-16 inches deep. The depth of that machine totally blows me away!
So, back to the subject at hand, yes, old machines can be fine but get a very good deal. If the price is too high break for the extra money and get a newer model.
Badger