Sram road spiders – are they interchangeable?

I have a sram s950 road carbon 2x crankset, however I want to convert to a single ring setup.

The spider unbolts from the crankset – could I simply swap the spider for a 1x spider?

Where would I get such a spider from?

Ah something like this:
http://www.ebay.co.uk/itm/SRAM-Force-CX1-40T-X-Sync-Chainring-W-Spider-Cyclocross-110-BCD-11-Speed-/321903903565?hash=item4af2f7c34d:g:rIYAAOSwMmBVyxeE

or this £30:

http://www.ebay.co.uk/itm/SRAM-Force-1-22-CX1-Crank-Arm-Spider-11-Spd-BCD-110mm-S900-S950-S950-Usable-/321954836853?hash=item4af600f175:g:33kAAOSwMmBV7Drr

With this: http://www.superstarcomponents.com/en/cyclocross-io-chainring-narrow-wide-style.htm

Do I even need one? or is one of my spider locations correct anyway?

OK I foun out that Sram GXP direct mount spiders and chainrings are interchangeable and what I’m after is this:

http://www.ebay.co.uk/itm/New-SRAM-X-Sync-Direct-Mount-40T-Chainring-6mm-Offset-For-GXP-BB30-PF30-/131567914133?hash=item1ea20f0c95:g:TjYAAOSwyQtVuuOA

Anyone know a cheaper 40T direct mount sram chainring? Seems a little pricey.