Doc,
Bonds are most certainly enforceable if they are put together correctly. The test is that the bond must not give the appearance of slavery. In other words is there a reasonable prospect that a person can leave at any time and not be bankrupted by the bond left owing.
30K over two years would be reasonable depending on the salary being paid, the employment prospects of the pilot and the cost of the endorsement upon the employer.
Of course the employer has to take legal action to enforce the bond and if the bond is only 10K it may not be worth their while because of the cost of using a lawyer to get it back.