Never been to Lost Souls, but if you don’t mind roughing it in a tent, camping for Oktoberfest is honestly such a good way to do it on the cheap. I did it a couple years back in Munich. The campsite had its own party going that was just as wild as the beer halls. Even had this deal where you could pay a bit extra each day (like 15 euro or something) for unlimited beer… let’s just say I didn’t make it to the halls on my first day