If you are just now building your pc. I would honestly start out the cheapest way possible and get used parts then from there I would work my way up to advancing and buying new parts or a PC already put together. Pc builds are expensive and can be pricy. You can buy basically anything from here Mercari or if you even have anything to sell you can do it through there which is full of private sellers.
Most of their items are pretty cheap and you can negotiate some of them down to get the right price for you. They do not get paid until the items are in your hands and you can test them then from there you can rate them on how the product is and then they get paid. If there is anything wrong then you can message them or submit a claim through the website and they will fix it with no hassle.
If you are looking for pc parts you should also check out New egg. This site is full of nothing but pc parts and it is like heaven. I love shopping on there and getting the best deals. Sometimes if you cannot find what you are looking for on there you can always go through amazon which is also a cheap route. I basically built mine and others using all of these sites.
If you do not want to build it you can get it built here or buy one that is already prebuilt! They have all kinds of deals and sales going on! Apex Gaming PCs