I have a ton of these things just lying around.
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Schrute Bucks are redeemable for 0.01 cents, or 10,000 to the dollar.
Unicoins can be bought for 9.99 cents (or 100 for $9.99).
So, you should be able to redeem 999 Schrute Bucks for 1 Unicoin, plus any fees your local currency exchange charges.
However, due to a disastrous and unforeseen bug, there are currently "technical reasons" you cannot buy unicoins from the website. You will have to rely on the black market for your coins, and there is generally a larger fee involved in doing so. A helpful guide to black market exchanges can be found at runawayguide.com.
You may also be able to use an intermediate currency of bacon instead of USD. Carlos Robles has opened an unofficial bacon/unicoin exchange. Please check with your local grocer for SB->bacon conversion rates.
I just checked at the local Apple (Jack) market and Schrute Bucks aren't currently accepted. Will check back again tomorrow. In the meantime you can try to convert them to Baccon Nuggets at your local change box. I hearded the mods will give a spring barbecue pretty soon, so I think the exchange rates will skyrocket in the next hours.