There are MANY rifles made in this caliber, and they reflect MANY different prices between them. Specify a make and model, or at least some distinguishing feature, if you want an accurate answer to this question - as is, the question is much too broad.
The .243. It's basically a necked down .308 Winchester.
100-400 USD
No sn data in the public domain.
100-300 USD
for a rifle it is thought to be a .50 calibre but a gun company made there own for there own sniper rifle the .408 calibre
308 calibre
Yes- it is called a SABOT ( pronounced say-bow). It permits a .22 caliber bullet (not cartridge, BULLET) to be loaded into a .308 cartridge casing.
No. The .243 is a larger calibre, and the parent case is the .308 Winchester, necked down to accept the smaller projectile. It's considerably more powerful than the .223.
No
Yes, but it might be called the xs7.
This all depends on the calibre of said rifle make and model :)
The Winchester Company introduced the 32 Calibre rifle in 1873. For it they created four different types of bullets including the Winchester 32 special.