Can anyone provide some feedback on the most affordable place for a US Citizen to purchase .IT domains.
livetodot will do it for a $50 setup fee & $25 annual maintenance fee on top of the purchase costs.

Can anyone provide some feedback on the most affordable place for a US Citizen to purchase .IT domains.
Are you sure that is allowed by rules for IT domain name registration at all?

Many european registrars would provide own eu adress for registrations where domain owner need to be eu resident, but in .it case is a bit different. Nic.it require paperwork - "letter of Assumption of Responsability (LAR)" with your ID number and personal signature which you need to send to Italy and waiting for approval.
They know to be very strict regarding this, so don't hope too much.