Personally, I use a Price Spike Limit that is around 150% of the average estimated earnings per card.  Using your example, I would set a limit of $4.50 for a GPU that averages $3.00.  That amount provides some room when values rise, but avoids work that is going to draw a lot of attention from other miners and is most likely based on an inaccurate data.

I really think that the x11 price issues on BlockMasters have hurt your earnings.  Since x11 is heavily mined by ASICs, it is almost never profitable to mine on GPUs anymore.  I have kept x11 disabled on my rigs and I have made more than $1 a GPU in the last eight hours on that one pool plus earnings on a couple other pools.  If you have already upgraded to 1.8.8 of Hash Auger, you may want to enable the MC Parameter for BlockMasters.  I have found that individual coin prices are better on that pool than the traditional auto-switch ports.  The only issue is that the C11-based coin ChainCoin has some issues on that pool, so you would want to disable the C11 algorithm on BlockMasters. 

A couple other tips to possibly help your earnings would be to try a slightly longer switch interval by increasing the Pool Refresh Rate to 15 minutes and to set the Min Price Switch % to at least 12%.  These settings can help you build larger shares in new coins and help offset the cost of switching work too frequently.