Foreign currency exchange rate Web services

All,

Looking for an easy (and relatively cheap) way to get historical foreign
currency rate Web service data.

So far, I've looked at:

xurrency.com (simple API but no historical data)
oanda.com (lots of historical data, but potentially not cheap)

Obviously, I'd prefer a simple REST API, but am willing to do SOAP if I
must.

Any feedback would be of interest.

Many thanks,
Wes Gamble