You should be able to find a cheapish MTB with perfectly good gear.
What are you prepared to spend? You should be able to get something decent compared to what you have new or even better second hand.
So not worth spending any money on a bike, which 18 years ago, was very good?
I agree with Ifor. Budget?
BTW both my MTBs are second hand. Decent bikes and I replace the components myself. I paid about £1350-£1500 for each but they’re both circa £2500-£3k new.
The trouble with spending money on an old frame is that the components, and MTB itself, have changed. For instance it’s probably a 26er? That’s a difficulty right there. I tried to do something similar, but eventually got a new 29er for less than I had already spent on gear for the old bike.