Forum Discussion
As Fred said above you should look for websites/stores that allow you to choose the parts and then they will assembly it for you for free of charge (mostly, some of them tied to spend a certain amount of money, some just to buy the parts from there). Here in Hungary we have tons of them and even in my city i know quite a few stores where you just walk in, point at this and that and bam in a day or two you have your custom built pc with the parts you've chosen.
Just do your research first because not many stores are user friendly and they might try to talk you into some crappy stuff like, "hey, its cheaper its only a year older but it should run fine" - not it wont, not all the time. So know what you looking for and if you are not sure bring a friend who is familiar with these things.
@LukkustafirAs others have said making your own can be a good way to go. If you're interested in it, perhaps the /r/buildapc subreddit is a good place to start.
it's easier than you'd think, and if it's a self build it makes maintenance (cleaning out, replacing or adding parts) easier as you're already familiar with the guts of your system.
If you do want to stick to a pre-build it's worth running it by the folks here or other tech communities for feedback before you commit. $800 CAD isn't a trivial investment and it's always worth making sure you get your money's worth.