howdy SU From my point of view its a work in progress. The costs of implementing an algo house are large but the initial R&D of the trading strategies and platform development are not - but I dont consider sitting in front of the PC and coding as a cost to take into account - besides its a skill worth having (for me) and not "time lost".
Spreads are a killer with high frequency trading or scalping ... instos offer spreads as 0.3 for USDJPY, 0.5 for EURUSD as typical and commission is very low too.