all very good questions with a range of answers.
There are a few free and paid sites like thingiverse, printables, cults3d, thangs, stlfinder, and myminifactory. There are some museums that also have models of ancient statues, buildings, and other things from history. I do have a few pirate sites I use and even sometimes just pay for it if the price is ok. A lot of copyright 3D artists are on patreon. The pirate site can range from free to a dollar or two, even right up to where the original artist charges, so you want to be careful with the pirated paid ones.
now the tricky part to answer is about how hard it is to do. it really depend on the person skill level with stuff. can you work on cars, or build a computer or does learning software scare you? some people can get a machine and it can be a pain others it works like a dream. now days the price for a good cheap printer can be in the couple a hundred dollar range, such as bambu labs FDM printer can almost just plug it in and go. no bed leveling, Z-axis adjustment, speed twerks. there is still some basic stuff to learn like what kind of filament you want to use but that's not to hard to choose from. FDM is the easiest to get into and the cheapest, with the lowest level to learn prep and clean up after, and it is the best from say part printing like door handles or bottle cap removes for people that have a hard time. the PLA filament is fairly tough. in the beginning it can feel a little weird learning a few things but really its not that hard to do. there are tons of youtube vidoes that walk you thought everything, it can just seem like a lot when you see all the settings but you really only use a few. almost each day the goes by its getting easier and cheaper to get into.
Now the real pain is resin printing, this one is a little more tricky, and the learning curve is there. I would not recommend a resin printer for someone that is just playing around or even as a hobby. unless you love tinkering and playing with stuff. You would think the software would be the same, but it's not. There are only a couple of companies that do it, and yes, they have free versions, but there is stuff you have to learn about the 3D model itself, the angle you put it on the plate, hollowing it, making sure there is little or no suction when the model lifts off the plate, supporting the model, and even the temperature can affect your print. It doesn't end there since you have resin cleanup and model cleanup. You can do this cheaply with just an alcohol bucket and a toothbrush or buy an ultrasonic cleaner (a low-temp one since it is alcohol), again you can just cure the model by leaving it in the sun but it is highly recommended to use a special UV setup to cure the model. but wait there is more if you dont cure it right and the model wasn't properly cured and hallowed and drained some time down the road it could crack open and leak. resin printer are 100% for highly detailed stuff, it can even do like skin texture and it can kind of printer faster then a FDM since it prints each layer at the same time it can print say 10 chess pieces at the same time, the FDM would take 10 times as long but the FDM will be stronger.
so in closing you can get a FDM get the bambu for 600, I got a anycubic vyper for about 400. 1 kilo of filiment is about $17, a lot of first time buyers will get an ender they are only 200 but you will have to learn a lot more since you will have to make adjustment and play around with things to get it working perfect, instead of the bambu and other more premium companies that come more calibrated. on the software is free at least the opensource ones. not 100% sure is bambu locked their printer behind a paywall or not.
well that was a lot more then I planned on writing but hey its done. if you have anymore question just ask. I'm not an expert on this and still learning stuff about it but I will be more then willing to help.