You need to go talk to them. Building a PC is like building a car in a way. The price depends on what you want. You want a super fast Ferrarr? That'll be expensive. Want a slow minivan? Not as much.
Price would vary greatly based on components. Best bet would be to call or go in and talk with them directly about your specific needs
I'm sure you could build a fully custom pc as for price couldn't tell you.
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