There are NO websites that provide any credible data for free. I repeat, NONE!
EIU has data which are available to individuals (not cheap).
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If you are serious, and buy the data, I am willing to help you do a proper comparison. It's not as simple as multiplying by a single factor and netting tax.
ECA provides the best data in my opinion, but normally only to corportes. Their basket has been updated and recalibrated more recently than the rest.
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Mercer is the MacDonald's of the industry. If you don't care about quality or rigour, you can get by with Mercer. Normally only sold to corporates. If you are just playing around, Mercer often publishes average top-level indices on their website.
You get what you pay for.
Disclosure: I'm not associated in any way with any of the organisations mentioned.