Anyone who is not a complete idiot and/or not lazy can do an unrealistically good job at recruiting in this game.
So, without further ado, here are the rules I am going to use in my dynasties for recruiting.
These numbers indicate the maximum number of recruits you are able to have in a class from a certain area, AS WELL AS the maximum number of recruits you can target from a given area in a given week. Also, any commitments you get from one of the areas reduces the number you are allowed to recruit in following weeks (basically, at any given time you cannot exceed the specified number of targets + commitments in a region)
Limits:
In-state: Unlimited
Region:*++ 5 total (Your region is the five closest states to your home state. If more than five are adjacent, pick a specific five to stick with for your entire dynasty.)
Florida, California, Texas:* The total limit is equal to your team's prestige (obviously if you are a school in one of these states the unlimited rule applies for your state)
All other states: Limit is equal to half of your prestige, rounded up. (1-2 stars = 1, 3-4 stars = 2, 5-6 stars = 3)
* - Teams in Washington, Oregon, Idaho, Nevada, Utah, and Arizona may NOT include California as a regional state, and can have only 4 regional states instead of 5. However, they can recruit up to 7 players from California IN ADDITION to whatever they are allowed according to their FL,CA,TX limit and other state limit. So, a 3 star team from Utah could recruit a maxiumum of 12 players from California (7 for the rule, 3 for their prestige, and 2 for their "other states" limit)
++ - All of the states in New England (Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont) count as one state. Thus, any school from any of those states gets unlimited recruiting from all of those states, and the New England region is only counted as one of the five total states when included in a school's region.
Note that the limits for regional and FL/CA/TX recruiting are combined limits for all states in the region. So, if your limit for FL/CA/TX is 4 players, you can recruit a total of four from FL, CA, and TX combined, not 4 players from each.
Also, limits can be combined if they overlap: If for example you are a 4-star program in Georgia, you could recruit up to 11 players from Florida: 4 for your FL, CA, TX limit, plus 5 from your region limit (Florida is in the region), plus 2 from your other states limit.
If you look at real recruiting classes, and consider that since there are limits on targets, you won't land all the out-of-state targets, I think these will be very realistic.
Also, I'll probably work something into the rules regarding coach prestige, so if you are a high prestige coach and for whatever reason end up at a lower prestige school, that gives you some benefit. (i.e. Lou Holtz moving to South Carolina)