You mentioned corn and beans. Do you have the equipment to plant and maintain them efficiently? Meaning a tractor, disc, row planter, and sprayer?
If so I say go that route as you can knock off 18 acres in a day or two if you know what you are doing. Also you need to rotate your corn and beans every year for disease and 'nitrogen' fixation purposes. So the plan to plant corn for screening your walk in will be short lived. You mentioned 2 fields. I would do corn in one and beans in the other every year.
To control costs we look for free or cheap corn (year old) from the NWTF, Pheasants Forever, farmers who didn't use all last years seed, the grain elevator/co-op, etc. We also plant 'bin beans' we get at the current bushel price from a local farmer (can't sell these of course, but they are for the deer only anyway).
We have spent money on fertilizing with P&K and urea. This is a big investment though and have had decent luck with just rotating the crops. You don't get the bu/acre as with fertilizing, but you need to remember you are feeding deer and not making a living at this.
If you have the equipment and 18 acres of ground, corn and beans are the quickest and easiest to plant and will draw/hold deer to your farm when neighboring food sources are consumed.
Now if you are planning on broadcasting corn and beans you can have some success but it is very time consuming and frustrating (been there).
It can also be very time consuming if you are doing a little of this and a little of that here and there. So that really depends on how close you are to your farm and how much time you can invest.
Good luck and have fun!