They work great, hold 8 arrows, and relatively available on e8ay. cost will depend on who is bidding, condition , and other factors.
The only down side to the spring arm quivers is that they tend to mar or dent the limbs where they make contact.
You can find the "converta-quiver that has a spring arm on top and a screw down on the bottom.
The screw attachment is for a side mounted bushing on the riser, but they made. a "converter" that let you mount it to the stabalizer bushing on the front of the bow, if it has one.
This is a better mount than a double swing arm, in my opinion.
Something else to consider is that the double spring arm models are not one size fits all. They were made with your choice of short medium and long.
If you get a long one, it is not going to sit well on a 54" bow. If you get a short one, it will not work well on a 66" bow. A medium might go both ways, but I doubt it wil lwork well on extremely short or long bows. Pay attention the the length, and this may not be posted as part of an e8ay auction. Some sellers don't know the difference, or which one they have. The one in TrapperDave's post above is the short model. It does seem to have about 4" adjustment range.