This being the first time I have managed to acquire an A+ prestige at division two, can anyone tell me about how high up on a ranked player, roughly, an A+ would allow you to go? 

It changed recently but it used to be in the 150 range....

It's different for different positions.  SF's and SG's are usually the positions where you can get the highest ranked players, PF seems to be the toughest.

You can also get very high-rated C's.

before it changed I was able to get a C ranked #122 and that was only with an A or A- prestige.

Believe it or not, my 1st year at NW Nazarene, I took over a D prestige program. I was able to get a #92 ranked Center, a #111 SF and #127 SF. All three of them were in my back yard, which makes a difference.  At Delta State with an A+ I got a #129 Center. I also got a #92 SG when I was at Minnesota Duluth - he was 280 miles away. I also had a #99 PG as a backup option.  This was a while back though. The closer they are to you, the better shot you have, especially if they prefer to stay close to home.  HOWEVER - I have found that the rankings really do not mean much, in my opinion. Some of my best players have been unranked.  I had a PF at Delta State that was unranked and started at 501 overall that ended at 790. I also had the #193 ranked Center who started at 458, but ended at a whopping 866 at Delta State. So, I don't pay much attention to the rankings. I think they are how that player is ranked at that particular moment in time, but if they have low potential, they will not be that good after 4 years compared to other players.

With a B prestige D2 I just signed the #155 SF and #195 SF. I think the guy ranked #195 will end up better though as he has more high potential categories.