This might be a little long, but I do shoot quite a bit. Probably more in year than most in their lifetime. You are just getting started congrats, it's a lot of fun. First off, keep going to ranges and shoot with other folks. Most are friendly and love to let others try out their guns,the more you can shoot other people's guns, the better. This can help you see the differences. This is not always an option, I understand.
As far as purchasing, for a semi I would go with Remington 1100 or beretta a400. Both are great. A400 will run you mid 1000 to almost 2000. Remington's can be had for about 1000 give or take a 100. I own five of them. The only reason I went 1100 was they don't make an a400 in 410. I shoot competitions with all the gauges.
For an over under you really need to save. Expect to pay 2000 minimum for a quality over under. Browning and beretta are good choices. I don't have experience with CZ so I can't comment on it. As far as yildiz, either save your money for a nicer shotgun or buy semi. Yildiz is not horrible for field gun, but shooting clays it's horrible. They kick way too much.
This sport can be extremely expensive or cheap depends on you. I used 1100's for quite a while, while I saved to buy my competition gun. I used to shoot a browning over under and it was great, probably all you ever need, but for me I wanted something more. So I bought the 1100's while I saved for a Zoli. You can get an 1100 competition model for about 1050 if you look real hard. 1100 are easy to maintain and can be repaired easily. Semis do have to be cleaned often since they are gas operated, but you should clean your guns often anyway.
Used guns; as some one said above don't be afraid of them. Just try to buy one you can look at,and inspect before hand. Gun ranges usually have personal flyers for people looking to buy/sell. This is a good way to get into a nice over under. If taken care of the guns will out last you, and the parts that do fail are easily replaced by gunsmiths: firing pins,trigger springs etc. if you look at Brownings stay way from the cynergy. Great feeling gun, but most gunsmiths can't work on them you have to send it to browning to fix anything. Ask me how I know, twice during major comps. The citoris on the other hand can be worked on easily as well as the beretta silver pigeons and 692, 682, a400, 391 etc.
Once again welcome to the sport! Go out and keep shooting and take your time. You will end up buying multiple guns if you really get the bug. And don't be afraid to ask people at the ranges questions. Most are super friendly and want others to have a good time.
