Frank tried Goodle finance first. The data is unreliable even for liquid ETFs like “TLT”. You get horizontal lines because of no data updates for days. Quandl is another obvious choice but their premium service is @50/month.
Yahoo continues its service so you can get data. The problem is that Yahoo, without notice, changed the API AND transitioned to unadjusted data. We need to take dividends into account so unadjusted data will not work for either reporting or ranking. We are now looking into Tiingo.com which is a fairly new service.
This has been a big problem for a lot of people and self directed investors:
Reading the forum you can see there is a wide open space for a data provider to enter get data from the exchanges and adjust it for a small fee ($5-$7/month). I hope someone jumps in. We would support them :)