It is 2026.  RTK guidance has been around for 20+ years in agriculture so there are lots of options.  If you are wanting to use it for row crop planting and cultivating you will be unhappy with WAAS.  A neighbor has FJ Dymanics RTK stuff in his 4450.  His rows are as straight as mine are with Trimble in the tractor and on the planter.  There is nothing wrong with a lot of used stuff but as has been said you'll want to work with a competent dealer.