If you are skeptical of the company's future, and the CEO is not to be trusted (and it is clear he is trying to take advantage of you), then ask yourself if you had 100k, would you invest it in this company? If the answer is no, then maybe you should take the buyout. On the other hand, how well do you live with regrets - if for example you were wrong and the CEO does not run the company into the round? If you really think the company will fail, then 100k is better than nothing.
How will the investors feel if they know that you would sell 5% of the company for $100k? Maybe this is your leverage: the investors will know the price of the buyout and since the investors know that you are very familiar with the company, then they will invest less. Therefore, the CEO should offer you a fair price for your shares.