There's always the naysayers who don't think you need any magnification. I honestly can't understand it. I don't know if they're shooting at car sized targets at those ranges or what but I can tell you that I barely consider 25x to be adequate for shooting varmints at 500 and I'd gladly take 50x if I could get it. There isn't any appreciable "wobble" when you're shooting at 500 yards from a bipod. There better not be, or you're wasting your time. Besides, the wobble is there whether you can see it or not. If it would make you miss at 25x, it would make you miss at 9x.
That said, I've used plenty a cheap scope in my life. My .204 wore a $125 10-40x Tasco for several years and it performed admirably (for it's price tag) until the day is was inexplicably and fatally off by several FEET at 100 yards. No big deal, it cost me a woodchuck.
However, that 10-40x was, in reality, more like a 10-25x or maybe 28x because it became unusable above that. The image simply washed out in all but the most direct, brightest sunlight and was completely useless above 32x in any conditions.
Also, compared side by side to a Bushnell Elite, it was obvious that the magnification was not correct. The image was noticeably (obviously) larger at the same setting in the Bushnell. That means the Tasco was probably more like a 20x max.
Currently, my .204 wears a 8.5-25x Mueller Eradicator that I got for $215. It is 5 times the scope that Tasco ever was and nearly on par in terms of optics, side by side comparison, with that same Bushnell Elite. The Bushnell is slightly brighter and clearer but not enough to effect shooting. Of course, the Bushnell is also more than 2x the price.
Long story short, I highly recommend that you find a Mueller, such as
this one.