As noted above, if you aren't changing to cams with a different base circle diameter you can just reuse the stock one piece pushrods. As a matter of fact, even if you change cams you can often find one piece rods in the correct length to work with the new cams. H-D sells some designed to work with various SE cams, called Perfect Fit Pushrods. The advantage of one piece rods is lighter weight and potentially better reliability (no heavy steel adjusting hardware, no nuts backing off, etc.). The disadvantage is the time and effort to remove the fuel tank and rocker covers/boxes to remove and install the pushrods.
Do you have any reason to pull the rocker covers, such as a seeping gasket? If you do, then save some cash and just reuse the stock pushrods since you need to pull the covers anyway. If not, then it becomes a case of labor costs. If you do it yourself, is the hour or two you save by not pulling the covers worth more to you than the $150 - $200 for the adjustables? If you're paying someone else to do it, get it quoted both ways. Probably fairly close either way.
Jerry