I have no issue with betfair with bets and my bet sizes are much higher than yours. All mine go on in the last few seconds before a race. I am also happy to take betfair SP when I don't get matched.

When are you trying to get matched ? If your doing it anytime other than in the last minute then you will have issues. Can you not use betfair SP ?

If you go the bookie route then you will find it frustrating if you are a long term winner.