Well, here goes. From what I know, ridleyi will cost you more than a Taiwan - maybe all of your budget. The ridleyi are still much less common than other species of the Orthriophis genus and as such are still commanding a higher price. Also, they seem to be more of a favorite when measured against Blues and Taiwans. I think they're interesting looking but I find the patterns of the Blues and Taiwans to be much more attractive. The ridleyi will also be a smaller species than either the Blues or Taiwans, so that is a possible consideration for you as well. From what I've read, you may also need to keep ridleyi cooler than either of the other two as they typically inhabit the cooler areas around caves, hence one of their common names, 'Cave Racer.' There are some smaller species of asian rats in the Orthiophis genus as well, such as the Chinese Beauties. A couple other regular posters here have kept them and can give you more info than me as far as those go.
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Matt Campbell
Animal Keeper, Small Mammal/Reptile House
Lincoln Park Zoo Chicago, Illinois
Assistant Curator
Wildlife Discovery Center at Elawa Farm
Lake Forest, Illinois