I think the lessons I take from italki instructors, by video calls over Skype, are as good as they would be if the teacher were sitting with me in person. I use two different instructors--in two different ways. I think both of these instructors have been completely professional and very skilled. 

You have to check with the particular teacher, but I think almost all of them have a reduced price for a short introductory lesson, and that usually? always? you are buying one lesson at a time, you're not committing to anything expensive.

The obvious suggestion is that you try a teacher and decide for yourself whether you think they are helping.

One mustn't expect miracles. For me, it's hard work and it's taking a long time. I think my teachers' rates are very reasonable, but week by week it certainly does add up. 

I guess I have to ask: what do you think could possibly be more effective than individual lessons, in which you spend the whole session speaking the language with someone who is a professional teacher?

It is certainly better than sitting in a classroom with fifteen other students and speaking the language only when the teacher calls on you!