ARs are not difficult to work on. The initial cost of a few specific tools is offset as you build more (and you will!). Welcome to the forum! If you're not going to do-it-yourself, check out Dreadnaught Industries LLC Guns Main Page
If you needed some actual machining work done, then I would recommend taking it to a gunsmith, but if you're just putting the gun together-that's not hard. You just need the right tools and there's several publications out there that can talk you through everything you need to know.