This is something that I notice, and I now assume that if they don’t advertise their pay, they are offering minimum wage. Most roles would be pleased to advertise if they were going to pay more than this.
However, you should never be worried about asking what they are paying. It is an important part of the process, and not something that they should have hidden in the first place. If you call them, you may be able to ask without the question being linked with your application when you decide to follow it up.