(Adds details on new car, paragraphs 13-15) * Cars open for orders now; many locations show deliveries in Dec-Jan * Pricing disappoints some investors and analysts * Musk emphasizes affordability amid rising competition and sales challenges * Affordable models crucial for Tesla's 20 million vehicle target and Musk's pay plan By Abhirup Roy and Harshita Mary Varghese Oct 7 (Reuters) – Tesla rolled out "affordable" versions of its best-selling Model Y SUV and its Model 3 sedan, but the starting prices of $39,990 and $36,990 were too high, some said, to attract a new class of buyers to the electric vehicle brand. CEO Elon Musk has touted the car as a way to tap a wider swath of buyers, saying last year that a price below $30,000, after incentives, was the key. Tesla is trying to reverse falli

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