Can I query a copy of a database without impacting performance of the primary?
You can do something like log shipping. Assuming you are already taking full and log backups on the primary server then using those backups to maintain a mostly-fresh copy of the database elsewhere will not impact the primary server at all (unless the storage for the backups is the same - which is a no-no anyway). You cannot access the database while logs are restored, but assuming you know when you'll be running your query bursts, you can schedule restore/standby operations outside of those windows (just know that the data won't always be in sync with the production copy, depending on the last log restore).

Your reporting copy can also serve as a warm standby to recover data in the event that the vendor or someone else makes a mistake in production - depending on the log shipping delay you can recover that data from before that mistake without recovering the entire database. I've seen this methodology used in several places, especially where a lot of cretins had ad hoc access to the database. :-)