With RTK extensions, and depending on exactly how you augment them, GNSS systems can get you to sub-meter levels of accuracy without too much work. But they're

With RTK extensions, and depending on exactly how you augment them, GNSS systems can get you to sub-meter levels of accuracy without too much work. But they're expensive. One of the least expensive devices in this space that I know of is the SparkFun RTK Express Kit. There may be better solutions out there, but you should also make sure that you know what the possibilities are with the old tried-and-true systems. Then you've got a baseline that you can use for comparison, and see how you can better that with other options.