My Tadpole trike, a TerraTrike Cruiser, is a great entry-level trike. I bought my wife's for 1100$ and mine for 800$ both were used. They are very fun--I've done 60 mile rides on it, but efficiency is lower than my stratus.
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2007 TerraTrike Cruiser (XL) Trike
2004 Rans Stratus XL LWB Recumbent
1999 Trek Navigator 200 21"