If it fits your bike it already has some age to it
DIY or have it fixed you will know what you have.

What does that 1000 bucks include do you know??

 

If you can still shift, then chances are the shifter arm might be loose on the shifter shaft. You can try to replace the Allen head socket with a Hex head and torque it down. It will buy you more time. In the long run, you will have to replace the shifter pawl assembly, because the shaft splines will wear out and not have good contact. It is a labor intensive job, thus the $1K. Depending on your budget, here are some of your options from cheapest to more costly:
1. tighten down shifter arm and hope for the best-- No cost.
2. replace shifter pawl assembly and change out to new design '94 later tranny pulley (I recently did this, using Jims shifter pawl assembly)
3. Have the mechanic do the job
4. Upgrade to 6 speed tranny/cartridge or 5 speed tranny--cost and still labor intensive

There are more options, I'm sure.

 

The first thing to check is the shift lever at the transmission, make sure it is not loose on the shaft.