If you are moderately careful you can do it by eye with a regular level. If you happen to have a laser level easily available, you can use that, it's easier. In either case, the method is the same - pick your starting point, and set the level on a stick (or tripod) above it. Measure the distance from the ground to the level, write it down, then use your eye on the level or the laser to mark a spot on the ground that is at the same height as the level. Go to that spot and repeat. Add up all the "height above ground" measurements and there is your rough estimate. This is (almost, but not quite) the same procedure that has been used by surveyors (with "better than average" care and tools) for centuries up until the recent introduction of "total stations" which allow them to get away with faster methods these days (and make "merely old" surveying equipment quite cheap, at least until it passes into the "expensive antique" era.)
If you actually have a rise of 10 meters in 200 meters, you won't need much range on your laser, as your "average" distance in that case would be ~40 meters or so (if you were as high as 2 meters off the ground - 1.5 meters is often more comfortable to work with unless you are very tall.) Working on an overcast day or in the early morning/late evening also increases the effective range of a laser over what you can spot in bright sunlight. One way to cheat is to use a white card and walk away from the laser holding the card in the beam - you can often see the beam that way when you cannot simply pick it out amid trees and foliage.
Edit: per comment on @Peter's answer, an example of a google earth elevation profile (complete with mythical cliff) - this may be the quickest method, if not of stunning accuracy: