Each person determines how far they want to go based on their budget and desires. There's no right answer.

For me, I cannot justify spending a thousand dollars for a single tank or say $600 for a basic kit that has to be built and doesn't come with lots of add-ons. But I might someday go for a single 1/6 scale tank! I currently have 5 Heng Longs and have or will spend an average of $200 on each for them for upgrades and spares in addition to their aquisition price. Everyone has different goals, people may have different goals for each of their tanks.