Regarding the first query, the patenting expenses in total (including professional fee) will be much higher than expenses involved in defensive disclosure. For example, IP.com charges about USD 225 for a 17 page disclosure.
Opting for defensive disclosure will establish your invention as prior art thereby preventing others from patenting your invention. However, you cannot prevent or stop others from making, using, selling, offering for sale, importing a product or process based on your invention disclosed.
Trade secrets have their pros and cons, and should ideally be used as a strategy when there is a good probability of maintaining the information as a trade secret.