Won't the cost depend mainly on where you want to be regulated? It will be very easy and cheap to be "Regulated " in Seychelles but then legally speaking can you market yourself in US? or other countries? "legally and openly " is the key word here. Perhaps easier to be an IB of a Futures FCM and with micro contracts + Exchange traded options you can not only match the granularity of the OTC FX but offer more products like spreads/ Options etc
too many resources need to be invested in such a thing, and it's not a fact that everything will go well and you will get any kind of success