Best way to find cheapest broker

Just comparing the spread might not be enough because you're ignoring the liquidity at the top price. Some brokers guarantee you a certain minimum liquidity at the top price (can be one million or so), while others don't. On top of that comes the execution time (which also depends on the distance between the server location and your office/home). We usually buy in a rising market and sell into a falling market which will always result in a price running away from you, that is especially true for any short term momentum based trading - means a slightly wider spread but a much closer server might be actually cheaper (highly depended on your trading style though).
Then there comes another problem. Cheap for which pair? I trade EUR/USD, GBP/USD and AUD/USD mostly, to get the most out of my trading I'd have to trade on probably 3 different brokers (but only if I keep volume based commission rebates out of the equation).

Tell you what mate, I had full hair before I started looking for perfect brokers, I'm bald now!

FPA is a bad joke btw, utterly worthless information, especially after the swiss national bomb.

Based in Moscow totally unregulated will not accept clients from UK or USA or Austria etc. Seems a pretty legitimate oufit

It has pros and cons, like everything else. It surely is a handy solution to the "all eggs in one basket" problem which might be especially important if one wants or has to trade on basically unregulated outfits or puts huge money with his broker instead of using custodian bank accounts or similar. If it is really cheaper depends on your volume and the brokers pricing structure though.

100% true. Cheap brokers are always low-quality as well. Better to pay more fees but receive quality execution.
They question is are there any brokers that really give access to interbank...

CRFIN is a self regulatory body which merely sets out a set of guidelines to follow. It is not associated to the government. If the broker goes bankrupt there is no compensation.

Anyway if it works for you good luck.