A test can run about $25, less or more, depends what you actually want tested.
The manure will help you out, so you shouldn't be in a bad situation.
If you are aiming for 140 bu corn, you'd probably want 100 to 150 lbs of N added, depends on what previous creop was, and how much manure you are adding.
Your 140bu corn will be removing 50 lbs of P, and 35lbs of K, so you'd really like to add that back in. Depends what youre manure adds back.
These days we don't get free sulfur from pollution any more, so 10 lbs of that is good. Perhaps your manure supplies that tho.