I was able to get the 5.0 Ah version (push, not self-propelled) for $279.00 at Home Depot in East TN.
Many of the stores (not all) have this item in Clearance, which can be checked here.
Takes a little leg-work to call around and check the prices, but I was able to find a relatively close store that had it clearanced at $279 ($120 discount) and after politely talking to the manager he agreed to match the other store's clearance price, even though my particular location has yet to role out the mower clearance sale prices.
Please note, many of the other locations had it clearanced at $369, so you will have to call and check prices.
Really a good price considering the battery alone is retailed at $249.00. So, if you are in the market for a spare battery already owning Ego equipment, this may be well worth it for you. I was replacing a 5-year old model, that had a LOT of use on it over rough terrain and was somewhat worn out.