You can purchase a policy to be effective for your required period of time or you can purchase it for less and continue to renew it without break, until the maximum period the plan is available for. That being said, if the policy expires, then you cannot renew the same policy. You would need to buy a new policy and in that case a new policy maximum and deductible would apply. In the case you have mentioned, if there is an elapsed period of time between your previous period of coverage and a new period of coverage, you would need to purchase a new policy, in which case a new deductible would be applicable.
Depending on the policy you purchase, the deductibles for travel medical insurance plans are applicable one time in a policy period, or once per-incident. For comprehensive coverage policies, it is a one time deductible and for limited coverage plans, the deductible is per incident.
Insurance rates are regulated by law. You can't find the same insurance plan for a lower price anywhere else