If I remember right, original bot is 300 pts, needing 5,000 to go to new bot (and the bats turning into level 1 bots if hit)
Level 2 bot (single hit) 500pts per hit, level 3 at 15,000
Level 3 bot (White-triple hit) 1,000pts per hit, level 4 at 30k
Level 4 bot (Black-triple hit/white bullet) 2,000pts per hit, level 5 at 50k
Level 5 bot (Black-triple hit/gold bullet/destroys bunker) 2,500pts per hit (I believe 70k for level 6)
Level 6 bot (Blue-triple hit(invisible)/gold bullet/destroys bunker)
Here's a screenshot of the game I played to get the info..