You can hit the gobble gum machine 3 times a round. The price increases every time you hit it. The price also increases every 10 rounds. A fire sales reduces all prices by 490 points.
ROUND 1ST/2ND/3RD
Round 1-9 500/1500/3000
Round 10-19 500/2500/5000
Round 20-29 500/4500/9000
Round 30-39 500/8500/17000
Round 40-49 500/16500/33000
Round 50-59 500/32500/65000
Round 60-69 500/64500/129000
Round 70-79 500/128500/257000
Round 80-89 500/256500/513000
Round 90-99 500/512500/1025000
Round 100-109 500/1024500/2049000
For Science -
110-119 2048500, 4097000
120-129: 4096500, 8193000
130-139: 8192500, 16385000
140-149: 16384500, 32769000
150-159: 32768500, 65537000
160-169: 65536500, 131073000
170-179: 131072500, 262145000
180-189: 262144500, 524289000
190-199: 524288500, 1048577000
200-209: 1048576500, 2097153000
210-219: 2097152500, 4194305000
Here is the equation/pattern to figure out the numbers -
1st gobblegum hit is always 500.
2nd gobblegum hit equation | X times 2 minus 500 (X x 2 - 500). X being the previous round range cost. Example 1-9 2nd gobblegum is 1,500. 1500 x 2 = 3000 - 500 = 2500. 2500 is the cost of 2nd gooblegum for round 10-19. 2500 x 2 = 5000 - 500 = 4500 is the cost of 2nd gobblegum for round 20-29.
3rd gobblegum hit is 2nd gobble gum hit cost times 2 (X x 2) Example Round 1-9 2nd Gobblegum cost 1500. 1500x2=3000. 3000 is cost 3rd gobblegum on round 1-9. Round lets go 50-59 2nd gobblegum cost 32500. 32500x2=65000. 65000 is the cost of 3rd gobblegum for round 50-59.
or X times 2 - 1000. X being the previous round range cost. Example 1-9 3rd gobblegum is 3,000 x 2 = 6000 - 1000 = 5000 is the cost of 3rd gobblegum for round 10-19. 5,000 x 2 = 10,000 - 1,000 = 9,000 is the cost of 3rd gobblegum for round 20-29.
*Note - I did this math all on my own! Who would of thought paying attention in math would have paid off playing zombies.