According to an estimate by Sterne Agee analyst Arvind Bhatia, he thinks that Zynga loses $150 for every new paying customer it acquires. This educated guess is based on the social gaming company’s confirmed $120 million marketing budget for the first nine months of 2011.

“Almost all of that [total] is for acquiring customers,” said Bhatia. “We also know that they had 3.4 million unique payers in the September quarter, which is up from 3 million at the end of December 2010. In other words, they added 400,000 additional payers and they spent $120 million to acquire them.”

This estimate suggests that ever new customer brought in costs Zynga $300, but that those customers only spend about $150 over the 12 to 15 months that players stay with the company on average. “That math won’t work for very long,” Bhatia noted.

Crucially, the company’s recent Hidden Chronicles on Facebook and Scramble With Friends on iOS haven’t been as successful as past Zynga games, and have battered the company’s share price as a result. “When we say that traffic hasn’t gone up despite new introductions, that’s telling us that maybe people are moving from one game to another, but you’re not really getting a lot of incremental people trying them,” said Bhatia.

“The really hardcore are, perhaps, finding themselves trying FarmVille, CastleWorld and CityVille. The newer audiences are trying and finding that this is all the same and leaving,” he added. “Again, the fact that there is such a small base of people who actually pay says that your risk is tremendous. This is spread out over 20 million people. You could say, ‘Oh yeah, 5 percent could get bored.’ Although, you only have 2 percent of your people paying, and God forbid if those guys get bored.”

Sterne Agee believes that the next year or so will be key for Zynga, as they try and find the next hit title in order to satisfy investors. “That’s the bottom line. Until they can find that, if it’s all incremental stuff that people are not really crazy about, it’s gonna be tough to put up the kinds of growth numbers that the stock’s multiple is implying,” noted Bhatia.