Well even if you get your Ufactor to 0, then you also get no benefits from the sun naturally heating your home in the winter which is beneficial. None of you window salesman mention that part.
I'm afraid that is absolutely incorrect Ben (forgive me if that is not your name). If you spend some time searching through this site, you'll see that passive solar gain is mentioned with regularity. The balance that you are looking for between a low u-value and a good shgc depends entirely on your climate, and the design of your home (ie: side that the windows are located, landscaping, awnings, etc).
I want to know about a "lower end" window that has structural stability. The alside excaliber looks like the frame is more solid than most, is this the case?
I'm afraid that for the most part, those two things are mutually exclusive. That's like saying I want a cheap car with 400 hp, good gas mileage, and great quality. There are trade-offs in any product that you purchase, and windows are no different. Unfortunately when comparing low vs mid vs high end windows, it is exactly the structural stability and "tightness" that will suffer. Most people think that its the glass, but that is not the case. Most manufacturers from low to high end all purchase their glass from the same handful of suppliers.
On the Excalibur in particular, my experience having sold and installed it is that it is one of the flimsier units that I've used. I've also seen a higher instance of service issues, primarily warped sashes, frowing sills, and air-leakage complaints. This is just my own personal experience, but from what I hear, it is a common complaint among pros.
My choices for entry level offerings would be the Okna 400, along with some of the lower lines from Polaris, Softlite, Homeguard, and Sunrise.
What products to people recommend to someone looking for a lower budget solution to the window game?
To say someone would need to replace a properly installed average window in 2 years is just dishonest. If your current windows are leaking heavily the gain you would get from a new window that doesnt leak vs the double the cost fancier version is minimal when you talk about how long to recoup your investment etc.
In terms of recouping your money in energy savings, that really depends on the differences in the u-vales, shgc, air infiltration, etc. In theory you are correct that small differences in these areas will take a long time to recoup. The problem is that the cheaper products are cheaper for a reason, whether it is the materials used, the manufacturing quality, etc. When corners are cut, the product will not maintain that performance over time, and lead to service issues/product failures, and/or overall dissatisfaction with performance.
Please don't take these recommendations as "salesguy bs" because its not. We are the good guys here, and we call them like we see them (some of us a little bit more gently than others )
The fact of the matter is, you don't need to pay that sleazeball sales guy $1000 per window, but the guys trying to make you think that you'll get quality for $200-$300 are just as dishonest. If you want a decent window that will last at a fair price (and installed properly by a competent company), you are going to be starting out in the $400-$500 per window range. There is just no way around that. It is no skin off our back if you want to go the cheap route, we are just speaking from experience and with the most sincere intentions. Please take that for whatever you feel it is worth.