There are various ways to have a read-only replica of the live database to offload reporting to, some of which are available in 2012 Standard Edition. If you don't need absolute to-the-second reporting then you could use log shipping with a short shipping interval to keep the copy updated, you could use replication, and so forth.
You may not even need a second instance of SQL Server: if you can install separate physical drives for the secondary database then you could keep the reporting copy on the same instances but different drives to reduce IO contention (though note that this will not help if your main bottlenecks are contention in tempdb or for CPU resource).
Have you researched where the bottlenecks actually are? You may be memory starved at times so thrashing the physical storage, in which case giving the machine more RAM could help a lot (on its own or in combination with having a copy on other drives) without needing a second instance. It may simply be that you can improve the design of those reports so that they get the same result with less effort too.
Of course availability groups will do what you describe and may form part of your uptime assurance & DR plans as well so if you need to upgrade for those reasons anyway by all means take advantage for reporting too, but do a through analysis of the problem to make sure there isn't a solution that isn't all of more optimal, less disruptive, and cheaper.