So, T/C has offered 5.7x28 chambered barrels for a while now.
Before they got in the game, a few custom barrel makers decided to play first.
A Remington short action can be converted to a singleshot "bench rest" gun with about $400 in parts from Midway.
All of the above are fairly pricey.
So how about the NEF/H&R?
Well, they don't (yet) offer 5.7x28 as part of their barrel accessory program. ( http://www.hr1871.com/Support/accessoryProgram.asp" onclick="window.open(this.href);return false; )
But what about a shotgun insert? ( http://www.mcace.com/shotguninserts.htm" onclick="window.open(this.href);return false; )
Elsewhere on the mcace site, they say "WILDCATS, ANTIQUE AND ODDBALL CALIBERS ARE OUR SPECIALTY!"...insert barrels have a standard length of 10 inches and are $65.00 each.
INSERTS FOR 410 SHOTGUNS ARE AVAILABLE IN:
22 LR 22 Mag 22 Hornet 218 Bee
If a .410 shotgun insert can handle a hornet or a bee it ought to be able to handle the 5.7x28mm.
The NEF Survivor in .410/.45LC can be had for less than $200.
Add an insert for $65-$95 (depending on length desired)
and total cost is still less than $300.
The extractor/ejector situation is probably less than ideal with an insert, so figure another $10 in parts and a fair amount of dremel work to modify the setup above to directly extract the 5.7x28 empties.
If the insert is long enough to protrude beyond the "host" barrel, it could be threaded M10x1 for the FsN-specific suppressors.
With a 10" insert and a modified host barrel along the lines of the SBX ( http://www.tacticalsol.com/store/pc/vie ... ategory=36" onclick="window.open(this.href);return false; ) one could have a relatively light, relatively short, relatively inexpensive single-shot with as much single-shot punch as a P90 that would probably be (slightly) quieter.