if around $1800 to $2200 is expensive for a direct bolt on is expensive then you have a problem. usually costs about $300 to swap turbos at most quality workshops. the HKS turbo option allows you to sell your standard turbo for $300-400. the GCG option means you either canibalise your existing turbo or better still you find a broken one suitable for hi-flowing.
some of the turbos you see on Ebay are name brand turbos BUT you then need oil and water lines, a new dump pipe, possibly spacer plates, intake piping modifications plus the cost of labour of these modifications. your $1500 turbo looks pretty pricey at the end of all this stuffing around.