Why do my nonstick fry pans 'bow up' and not make good contact with my flat top stove We recently bought a flat top (glass top) stove to replace our standard electric stove with the coiled "eye" heating elements. The flat top is certainly easy to clean, and if you have a boil-over, it does not fill the pan under the burner and spill into the interior of the stove - all pluses. However, I find that every nonstick fry pan I have has developed a 'bow' or curvature. That is, the center of the pan is bowed out, so that when the pan rests on the flat top stove surface it does not make great contact anywhere except right in the center. All the edges of the pan curve up, away from the heat. Thus it takes awhile to heat up, and probably wastes lots of heat. This bow may have been present with the regular "eye" coiled heating elements, but it wasn't as noticeable because they were not as absolutely flat at the glass. I even bought a new nonstick skillet, and swore to never use it on more than medium high, to keep this bow from forming. Still, it has bowed over a few months use, so even on the new skillet this problem remains.

My question is, what can I do to avoid or fix this problem? I keep wishing for some high heat tolerant and conductive thing to put between the stove surface and the pan so I get good thermal contact (something like a thin bag of sand, but with the bag made out of a material that would not be destroyed by the heat). Or am I just buying cheap nonstick cookware, and if I really spend a lot on a frying pan, the problem would not occur. This last part is really my question. I have spent $30 on a frying pan, only to see this same thing occur. If I spend $200 on a frying pan, will that solve the problem (will it not do this bowing thing), or will I get the same results in a few months? In case it's relevant, I live in the US (North Carolina).
The reason that cookware warps is that it is has too thin of a base.  When it has been heated to a high temperature, it warps upon cooldown.  The only way to avoid this is to buy very sturdy, heavy duty cookware.  You need to look for something with a very thick and heavy base, then you will have no issue.  

And don't think that it will put you in the poor-house.  I bought new pans 6 years ago, and they are still fine.  The most I paid was $30 for my 14 inch pan.  Every other pan I bought on sale for 10-15 dollars.

As for pots, you should be able to get a good set of Lagostina (or comparable brand) which are certainly not professional, but they will do the job.  They will not run too much money.

Just reread your post, originally missed the bit on the end.  You absolutely do not need to spend 200 dollars on a pan.  Just do your homework on the brand you are buying.  Where do you live (country, I mean.  Not trying to be too personal)? I may be able to suggest some places if you live in North America.