If it is new in the box, 450.00 is a good buy. However, you might possibly have sold the .45 auto for more so they may have skinned you slightly depending on what make it was and the shape it was in. The used, or "Like New", 7.5s vary in price from shop to shop; but, if it is indeed a newly manufactured gun it's worth more than 450.00. If it is an unfired old model it is worth more--a good deal more to the right buyer. I have seen used blued for 600.00+. Check with Ruger, or post the SN here and someone will know what year it was made. Rumor has it that there may have been a few longer barrels at Ruger and they made them up and moved them out. I have no idea if that is accurate or not. The seller should have had some provenance on it. If it was not new, there was a fired case after a Gunsmith checked it out or some such and hence the date.
Great guns, regardless. Enjoy it.