Accurate way to Measure Swing Speed on the Cheap

I know that I have a pretty high swing speed, but would like an accurate reading to see if I really need to play ProV1x's. I am quite tall and have super long arms which leads me to believe I have a big swing speed but I have a tendency to play the ball forward on my stance on my irons which seems to kill any kind of spin control on the ball. I'm tossed between whether to slow my swing, or to reconsider the ball I play for increased control. I'm not flush, so a Cheap way would be fantastic.

Just because you have a high swing speed doesn't mean you HAVE to play the ProV1x. I know that I was playing NXT's and Bridgestone e6's (depending on what was cheaper) until I was a single digit handicap just because I lost them too frequently to spend $48 a dozen on balls. Or, if you were asking to see whether you were swinging fast enough to even use a ball like that, I'd say go for it if that's what you want. Hit whatever ball feels good to you and won't break the bank if you lose it (I still get upset when I lose a ball, even though I get the ProV1's for only $32 a dozen now) or hit it into a hazard.

Go to a Dick's or Golfsmith and ask them if you can use their equipment to get a reading so you can decide what ball to play.  I wouldn't expect them to charge anything for it, especially if they thought you might buy some balls, but if I were you I think this would be my first strategy.