I don't think there are any decent reasonable quality meters for less than 100euros.
Some units can cost about 200 euros, with the more professional units can cost over 500 euros....
Apart from a basic "beeper" unit.
If your dish is constantly getting knocked out of alignment then there are other things to do:
secure it better, move it out of harms way, or your dish is simply a poor make with poor bracketry or poor support.
YOu can use a marker pen to mark all the crucial points that may move out of alignment, and sometime I have even seen a weight on a set length of string with a marker on the floor hanging from the LNB, so that it can be aligned back.
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