Again: what type of .45acp do you want? Hammer fired or striker fired? Metal framed or plastic framed? DA/SA or SA?
I assume it was a .45acp you were talking about, and not a .45lc?
Also, when you say $500, is that the firearm price you can pay, without counting the sales tax and DROS fees? Or is that the 'out the door price'?
If you are talking $500 'out the door', you are probably looking at the RIA 1911 as one of the few new .45acp pistols that would fit within that financial constraint. However, there are other used pistols you might find that do fit.
If your $500 is a ball-park, and not counting taxes/fees, there are a few other new options that are good, and most have been mentioned.
In a 1911, the RIA products are pretty good for the money. They are not as refined as a $1200 pistol, but they cost less than half of that, and they have a lifetime warranty. Most owners report good things, as long as you don't expect it to be as well fit or precise as a $1200+ gun. In other words, don't buy a Honda and expect it to perform like a Porsche. But both are good products.
I had a small issue with my RIA Tactical after the 500 round break-in period, called RIA up and sent it in. 3 days after they received the parts [I had Arnel install nightsights while it was there] it was finished and back to me. It is now as precise as any carry/duty .45acp [and I have 5 that fit that description]. I do highly recommend you check them out. I think I am among the few with problems out of the box, but their customer service was top-notch, and it is lifetime!
Another new pistol in the $500 range that wasn't mentioned is the Ruger P345. I'd check that out if you are interested in a DA/SA hammer-fired .45acp that is reliable and combat-accurate. Ruger may still make the P90, which is a metal-framed DA/SA .45acp that also has a great reputation for durability and combat-accuracy. I've had the Ruger P97 [made 1997-2004] since 2001 and find it a very reliable and surprisingly accurate gun. You can pick those up used for about $300 or less frequently. I like Ruger products, as they are like a chevy or a ford: aimed to be reliable and function, yet be affordable for the average american.
If you are REALLY stuck on the 1911 platform, the RIA is the only one I'd ever recommend to a friend in that price-range. And, as was stated, it won't be as refined as the Beretta you are used to.
As to used purchases, I have no problem doing so, as I am able to detail strip about any handgun and can fine-tune parts as needed. If you are not technically apt, if you find a field-stripping of the handgun to be cumbersome and frustrating just to clean it after each range trip, DO NOT BUY A USED GUN! You may get lucky with the used gun and find it has no problems, but you may need to do repairs fairly quickly.
For example, the Sig P220. I would hesitate to buy older Sigs if I didn't know how to do repairs. At some point Sig went to a solid block slide, but earlier models were usually a folded metal slide and a breech that was pinned in. The breech pins on folded metal slide Sigs need to be replaced every 4000 rounds. If you buy an older Sig with such a slide, it would be wise to replace those pins [and all springs] right away so that you KNOW when to do it next, and don't have pins shear off. But, if you don't know much about the design and repair characteristics, a shooter could buy a gun and operate it past those repair stages and then experience problems.
And used has no warranty. I am so unconcerned that only about 37% of my handguns were purchased new. Used doesn't have to be a problem, as long as you learn how to evaluate the condition of the handgun and you are willing to make repairs.
It is like buying a used car: you can make wise purchases or you can buy a lemon.