Bah! You can beat the Midgar Zolom at level 14-15 and get Beta in the process quite easily!

I just did it recently. All you need to do is link of elemental materia to fire materia on your armor, and have that person with the enemy skill materia. I used Barret because of his high VIT.

Use a gravibomb (I forget the name, but it's a demi item), use your limit breaks and when he uses Beta, Barret will be the only one to survive. So get him to use Beta back and finish off with his limit break.

Oh, it's also a good idea to put the characters in Sadness (by using tranquils or something). That way you don't take as much damage.

Easy! Don't need to be level 99 for it!