on your website someone estimated $55.00 per sq ft to build a screened in porch - would $55.00 include everything from the foundation to the roof top?
Have plans made and call local contractors to bid on the job. Costs will be based on region, construction details, sitework needed, etc.....
One size does not fit all. You might get someone in, without plans, to give you a ballpark figure if you spend some time detailing what you want.