I ran through the Michel Thomas 8 hour audio course, then 3 semesters of evening class at my university (run by the language dept). That was about 60 hours of class time, 2 hours a week. By the end I would have been comfortable going for B1 with a bit of study. In terms of course level I finished up working on B2 level material. If I was doing it again I'd look at the Instituto Cervantes. I had access to grad student pricing, but even so it cost about 200 a semester.
At the time I was also dating a native speaker and we would watch Spanish TV with English subs as well as English TV with Spanish subs. I still have a lot of friends who are native Spanish speakers which helps.
No idea about Fluenz, sorry. One of my friends used Lingoda for German and seemed to have a decent time with it. They also do language marathons where you get a significant discount if you do daily lessons, but it's easy to miss one and then you don't get a refund.
I think the takeaway is that classes sometimes don't feel that useful at the time - I would often be doing homework the night before, or on the train, but it made a massive difference speaking to people regularly. The main benefit is it offers a structure that's difficult to get if you talk to strangers or even friends, or if you buy a textbook.
Professional (and experienced) teachers are careful to not use vocabulary that's beyond your level, but at the same time a good class will be taught solely in the target language. In that sense I would seriously look at Lingoda if you can't attend evening classes. You get structured lessons with real people with very flexible scheduling. I don't know what qualifications the teachers are required to have though, and it's important as a beginner that you have people who know how to teach (and aren't just regurgitating the material).
For Spanish, Instituto Cervantes (similarly for German you have the Goethe Institute) is the de facto international language school and you can mostly guarantee the teachers will be good.
Much appreciate your feedback, which is very helpful. I agree with you on balancing structural benefits of classes with vocabulary and other benefits of conversational practice with native speakers. I haven't heard of Lingoda before - will definitely check it out and keep it in mind.
At the time I was also dating a native speaker and we would watch Spanish TV with English subs as well as English TV with Spanish subs. I still have a lot of friends who are native Spanish speakers which helps.
No idea about Fluenz, sorry. One of my friends used Lingoda for German and seemed to have a decent time with it. They also do language marathons where you get a significant discount if you do daily lessons, but it's easy to miss one and then you don't get a refund.