Don't cut yourself too short on the shoes.  Improper support can lead to
back problems and you definitely don't want to add to yours.  Look for the
best you can afford.  Good shoes don't have to cost an arm and a leg if
you're willing to go with last year's model, etc.  Watch for discontinued
styles and other sales.  I've had lower back problems since childhood and
start feeling pain in the lower back when my shoes begin to wear down.
With the damaged disc I would imagine you would want lots of cushioning to
avoid jarring.

If you are willing to spend $14 on walmart shoes, would you be willing
to spend $20 or $25 for a HUGE difference in quality?

If you can swing it, then what you do is keep your eyes open.
Around my area we have Rack Room Clearance Outlet store - where the
"last season" shoes go at the end of the season.    I can pick up
brand new running sneakers for $10 - $25 (depending on my luck).    It
takes effort to watch the store and when I find them, I'll buy a
couple pair at a time.

Another tip is to watch your local department stores, or places like
Fashion Footwear.  WHen they have their sales you can many times get
new shoes for up to 75% off (putting them down into a $20 price
range).

Finally, I'll watch the local outlet stores for their sales and can go
into Reebok or Nike and get the sales where you buy 2, get 1 free
which, once again, can bring down your "per pair" price to the $20 -
$25 range.

Reebok, Nike or New Balance are the brands to stick with.    I think
the common consensus is New Balance makes the best shoe.