I normally encourage people to learn how towork on their own cars whenever possible and save thousands. An exhaust manifold for a rookie is probably not the best intro though. Everything on exhausts gets rusty because of the heat, so there's a good chance it's not just a simple "loosen bolts, take part off, put new part on, tighten bolts" kind of job. Rusty exhaust manifolds & rusty nuts holding them on, you're more likely to round off the nuts or snap the studs and then you're quickly stuck with an un-usable car that is way beyond what a rookie can handle fixing. You'd need to be prepared to weld a nut onto a broken stud to get it out, or drill into the center of a stud and use an extractor without fucking up the threads in the cylinder head (or you do fuck up the threads and then you're installing heli-coils, and if you fuck that up you're buying / rebuilding the upper half of your engine.

Basically, you might get lucky and it'll go OK, but it very quickly can spiral into a job that a rookie doesn't have the equipment or experience to handle. Only try this if you have a 2nd car you can get to work with if something goes wrong and ends up taking a lot longer, and if you have spare money to the car towed and fixed at a shop if you get in over your head.