The chances are that the low end monitors you are trying are displaying too bright.
The reason for calibrating is generally to get a better match to prints as with prints you can control what the end user gets to see.
If you are processing for web display only then calibration is significantly less important as you have precisely zero control of what the end user gets to see - most people will have un-calibrated displays that have never been adjusted since being un boxed.
My recommendation would be to get your sample images printed out at a decent size (say 12x8 or larger) from a reputable lab and see what they come back like.


