Worth is a personal idea, I think.
For the pros that offer services, they tend to be fairly expensive but also better experiences, in my opinion. They do this more for a living and therefore have more experience and also are going to provide better overall service. Amateur models are usually less expensive, less experienced and more difficult to work with but also tend to have more interesting responses, in my opinion. Of course, Im only really talking about fetish and tickling models here. You'll probably have a much different experience if you take a route with first timers or non-models.
In terms of worth, your mileage is going to vary greatly depending upon what you consider a worthwhile monetary value and who you choose to deal with. Life happens, some models are less reliable than others, and your preconceptions about what the experience will be like will often have an effect on how much you enjoy it at the moment and how fondly you look back on it.
As for expectations, again your mileage will vary per model. Most are very accommodating. Just remember you're dealing with a person and that this is a job to them. I recommend that you be courteous/respectful, thorough in describing your expectations but short of word (try not to pester them too much). For example, ask about bondage and limitations, or any additional things you want to incorporate into the session before the session. When you meet up, establish what is off limits, safe words, breaks, etc. if necessary.
Oh, I also highly recommend reyafet
