You could focus on colleges you can make day trips to their camps. You will have to determine whether the camps are money makers or legitimate prospect camps. These usually run $150 to $250.
You could email colleges explaining your sons interest, your limited exposure budget and their suggestion for the best way to get in front of them.
Your son could go the JuCo route and rely on the JuCo program to get him to the next level. You would need to make sure he attends a JuCo with the ability to give him exposure to the next level.
He should ask his high school and summer ball coach if they can help with contact in any way. Even though my son made all contacts through travel his high school named colleges he knew coaches and was willing to call on his behalf.
If your son is good enough a travel team may be willing to finance some or all of his participation.
Watch this site for teams looking for additional players for a tournament.
If your son wants it badly enough he can get a job and put all the earnings towards his recruiting budget.