I wish to buy a economic (cost effective) laser vibrometer to measure the precise mode shapes of the structure. Can anyone suggest me other than polytec laser vibrometer.
I do not know what budget do have, I guess that vibrometers which can capture a grid of points are typically expensive. One model that was used in my previous lab was Polytec PSV-400. They use it to capture mode shapes and lamb waves, like in this paper: Article Self-focusing Lamb waves based on the decomposition of the t...
As Jeremi mentions, these things are quite expensive - when new.
Suggestions
Try eBay and see if you can find and old laser vibrometer that can do what you want
Consider using a laser position sensor instead. Some of these are accurate enough (micrometer resolution), go up to high frequency and they are much cheaper - in particular when you find a used one.
Note that laser vibrometers were hot technology in the 90's. Not all of them were that good. As they are 'pre-internet', it may require some digging to find data sheets.
Patience in buying allows you to wait for the unit you want. If so, you need to have the cash ready to strike the deal quickly.
Last - you can haggle over the price with most eBay sellers.
I scanned internet a bit and found this Thesis work.A 5 EURO, component cost, laser vibrometer