In Ch 1, Mr. Morland is described as

"...a clergyman, without being neglected, or poor, and a very respectable man, ... He had a considerable independence besides two good livings."

The details of what Mr. Morland is willing to do to set up James in marriage are

"A living, of which Mr. Morland was himself patron and incumbent, of about four hundred pounds yearly value, was to be resigned to his son as soon as he should be old enough to take it; no trifling deduction from the family income, no niggardly assignment to one of ten children. An estate of at least equal value, moreover, was assured as his future inheritance."

So, Mr Morland is prepared to resign one of his two livings to James, thereby cutting his own income by £400 - as JA says, no trifling deduction from the family income. Only remember that that all four Dashwood ladies were to get by on £500, this seems a substantial amount of money, especially with nine children still at home.

I assume the estate mentioned is one which will go to James after his father's death? So eventually his income will be £800-1,000. Mr. Bennet's income was £2,000, yes? This seems a more than comfortable income, certainly much more than Isabella's family has - there is no talk of her bringing a dowry or portion to the marriage and yet she is very disappointed.