A bath drawer does not have to take the weight and abuse we often see with a kitchen drawer that's filled to capacity with the heavy weight of pots and pans, dishes, etc.
I've had no issues using the cheaper big box slides for baths. Bath drawers might be used a lot, but there is little weight in the mostly smaller drawers.
Older vanities were wood on wood. Even the cheapest of guides will shine in comparison.
If you don't have time to do it right the first time, when will you have time to do it over?