The other day I was writing a review of one volume of a 21 volume concordance to the targum of the Prophets. The price for the complete set was over 2000 USD. Although full of admiration for the work of the editors I felt unable to commend it for widespread purchase because there is, freely available, the text of all the major targums already online. I bring it to attention here, because the site may not be the most obvious one.
The basic site is the Comprehensive Aramaic Lexicon. On the front page click on 'Search the CAL databases' and then follow the link to 'Targum Studies Module'. All words are fully parsed and you can read in Roman or Aramaic script. The whole site is therefore accesible to those who do not know Aramaic. You can also pull up multiple targums (with the Peshitta too). They have a great team involved: Stephen Kaufman, also a poker legend, Joseph Fitzmyer, who needs no introduction, Michael Sokoloff, who is producing an English version of Brockelmann's Syriac Lexicon, and Jerome Lund, who has recently produced a concordance of the Old Syriac Gospels.