You will be sending SBD to bots everytime you want to buy their votes. I think what you are asking if they are a sort of subscription where you will only pay one-time payment and get continues upvotes on your post? If that's what you mean the answer is No. It's 1 bid = 1 upvote.

But if you are looking for a sort of subscription you may subscribe to @resteemvote, my very own project where you can send 1 SBD and receive upvotes on each of your post for 1 month. You can check the details here