jeetuagr You would have to contact MS to get discounted rates for your organisation. I know non-for profit organisation gets special benefits from MS and you're organisation might be eligible. O365 is Office 365 service and E5 and E3 is the level of its subscription. Check it out here.
Office 365 Enterprise E5 includes Power BI Pro but E3 does not. You can take a look at this document to see the differences between Office 365 Enterprise E3 and E5.
Microsoft Employee