Logic says that the longer a project takes, the more it should cost. But due to resurfacing not accruing any labor costs and the short timeline help make it the most cost effective element in any bathroom project. There is minimal labor, and that means minimal time the bathroom is out of commission.
Although the cost of a new tub can be relatively inexpensive, greater costs accumulate with a tub replacement job, including the costs of time and money with tearing out the old tub, additional plumbing work, removal and application of tub surround, and other unpredictable expenses. The quality of the older tubs in general are superior to new tubs, which tend to be made with lesser quality materials and craftsmanship. Therefore, you will be better off hiring a professional to reglaze your higher quality, older tub, than replacing the tub with a modern, lower quality tub.