I also get a lot of flack for this, but if you're just going to ride around the neighborhood, an inexpensive bike will do. BUT, if you are even considering riding off-road, they just won't hold up and the weight of them will make you work twice as hard.
There are a ton of choices of quality bike available in the sub-$300 range. A lot of shops don't stock non-suspension bikes, because nowadays, everyone wants at least a suspension fork. But if you flip through a couple of catalogues, you'll see their entry level bikes offered in a non-suspension model. They usually run in the $250 price point.
Then, there is always the USED option. You can usually find a $500-600 two year old bike for $250-300.
L8R
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger