Since these require specialized programming and supplies from the manufacturer, and typically they will not help those who buy these devices used, there are really no options for a low cost walkaide device.
There are many exercises you can do right at home for leg weakness and drop foot that will likely be effective for you. These can be done without any specialized equipment or with low cost, easy to acquire gear. You can get lots of info on both these options on the web and YouTube.
Yes, it will take lots of time and hard, hard work but the results you get should be worth your effort.
If the exercises you are doing are not helping you, change the exercises you are doing. Consider:
which is an online service that specializes in helping those with MS and the type of issues you are experiencing. I also recommend the use of a vertical climber, an inexpensive exercise machine that I find targets my weekend left muscles better than any other exercise I do. Someone here on TIMS posted info on this service recently and signed up for it.
I also just found this recumbent exercise machine which I am considering getting:
Although I have an elliptical and a stationery bike, I find neither targets the muscles I need strengthened and think this one will do a better job as the leg motion is different. It seems to offer a more natural walking/stepping motion than other machines.
You can see a video demonstration of the machine here:
Take a close look at the foot/ankle movement in the video, this is unlike any other exercise equipment I have seen.
Here is a link to the manufacturer's website detailing this product: