Of the games discussed so far in this thread, I own several, here's my take in order of depth:
TSPP: One of the deepest ever! Unlikely to find at $3500.
RBION: Great game! Deep rules. Often many different ways to play strategically in any given situation. Atlantis and Frog Frenzy can be very difficult/rare to get depending on game setup.
TFTC: A slight edge in terms of depth over LAH. Not a family friendly theme.
LAH: Lots of great mode and the possibility for strategic stacking. Wizard mode is a bit meh unless you get Caker's code.
NBAFB: Great rules and a very fun game for casual and experienced players alike. A lot of modes and getting a single ring, let alone 4, can be challenging. Not much strategic stacking, but there is definitely a lot of opportunity for other strategy in how to play. That being said, the rules are probably more broad than deep.
Maverick: Wizard mode is not easy to get to and there is definitely a lot of strategic possibilities, but with only 5 modes plus the poker hands, I'm not sure it's a deep rule set. However, it may be one of the deepest pins strategically for such a "compact" rule set. A single strategic misstep can really impact your score, but you always have the opportunity to score big. For some reason, the basic rules are a little difficult to grasp unless explained. 17 drop targets! Great bang for the buck.