looking at adding a jack plate

i got a 2000 model boat with a 90hp johnson is it worth it to add a jack plate to my boat

What kind of boat? Length, manufacturer, year?

If you haven't already, try moving the motor up (or down) on the transom before you go to the expense of adding a jp. I ran a 16 1/2' Javelin w/115 Fast Strike right on the transom, playing with engine height and props until I got it running as good as one could hope for that rig. IMO, from a practical standpoint, I doubt additional setback would provide appreciable benefit on a rig in that size class(unless of course you're rigging out for racing, and hanging a bigger motor).

Nope. Take the money and buy some tackle.