Re: Windex vs. anemometer opinions...
You don't mention which Bay you're sailing. I sailed on Barnegat Bay for many years with only a windex and though I now have both wind speed/direction and boat speed sensors, the windex still gets plenty of use. So, I would say, if money is tight just use the windex. You can buy a handheld anemometer, if wind speed is something you think you must know.
Boat speed given from a GPS is speed over ground. To get speed through the water you would need another sensor. The difference is the effect of any current present. You can obtain a trailing knotmeter..I have one on the boat as a backup but I forget who makes it.
IF you don't sail where there are strong currents, you should be fine with the GPS..