Most likely at those prices, the LPK will be a common mil spec kit such as DPMS etc. and truly won't matter too much ... He should still be up front with you, however.
My guess is that he can't tell you at the moment because the actual brand of the LPK (assuming that is the part(s) we are talking about) would depend on the deal and availability he finds when purchasing. another area to cheap out on is the barrel - tons of options, different specs and materials.
If you're worried, ask him for options or a recommendation. That's why some build rather than buy - to get specific parts for customization.
My advice is sit down and put a lot of thought into what you really want, what you are going to use it for and start prioritizing what is most important to you. Otherwise you could become quickly dissatisfied with what you have and create a whole new addiction trying to fix it. The possibilities are endless with the AR platform, unless your finances are, be slow and deliberate. Most of all have fun.