Entry level - IMHO it would mean, what is the cheapest system that yopu can get in in order to enjoy 5.1 Home theater, so I would say a Yamaha RXV357, Small Yamaha Speakers , small yamaha subs etc.... this is your ENTRY into the 5.1 system from Yamaha
To add an entry level 5.1 system from Yamaha may cost 30K, whereas an Entry Level from Harman Kardon will cost 50K, both are entry level systems, but from different brands at different cost, An entry Level from Revel will may cost you in excess of 100K, again these are entry levels at different cost from different brands... Mid levels imho would be the model in somewhere between the cheapest model and the most expensive model from the SAME brand.