The vast majority of employer-employee relationships are not contractually bound so your employer isn't doing anything at all unusual in that regard. The majority of employer bonus programs are also discretionary; that is, if the employer elects to have a bonus plan, they can pay or not pay as they please and/or as funds are available. Seems foolish to me that any employer would announce bonuses to employees when they clearly don't have the money/funding available to pay them.
You can try suing in small claims court and see what a judge decides but even if you get a judgment in your favor, you still have to try and collect it and if the company doesn't have the money, then they don't have the money. No, you and your co-workers should not pursue a class action suit; this is way too small potatoes for that. It's a small claims court matter.
You have nothing to lose by suing in small claims court but frankly, it doesn't sound like you should ever count on receiving this money.

