I have a 1990s vertik 2 it's the mountain bike one and I am wondering if I could convert the rim brakes to disc brakes if so what are good budget options
You would require new wheel hubs with a disk rotor mount, and you would need a fork and a frame with caliper mounts.
Once you replace the fork, frame, and wheel hubs, its not economical.
Instead, shout yourself to some new rim brake pads. Good kool-stop ones will improve your braking and it feels like a decent upgrade, for much cheaper.
There used to be an adapter kit made by Brake Therapy that would allow you to mount a rear caliper on a non-disk frame. It's the only adapter I've ever seen that looked reliable enough. I believe they're out of business though.
That would still leave your fork needing to be altered or replaced and replacing your wheels to be disk compatible. So no budget options really exist. Keep the bike as it is. Looks like a pretty decent bike from the era. Find something newer that already has disk capabilities. You should be able to find something used that's decent for under $200.