Seeking for the cheapest liquid asset

SPY
Go with commission-free broker.

 

For futures, using your definition of "cheap," the cheapest markets to trade are the bond market and the S&P.

For spot, the cheapest market is the S&P 500 ETF, SPY.

 

NQ is $5 per tick.

 

Im posting my orders through FIX API and as far as I have researched this there are no brokers offering FIX with no commissions, but hopefully Im wrong