Spend, expend, disburse can mean to pay out money or an equivalent of money for something or in expectation of some return.
Spend is the ordinary term; it may be used regardless of the amount dealt out in the purchase of something.
In intransitive use it requires usually an adverb or adverbial phrase to indicate the extent to which money or, by extension, its equivalent, is paid out.
However the word is often used with so little implication of an immediate or direct or commensurate return and with objects so remotely equivalent to money that it comes to imply a using in such a manner as to exhaust, drain, or deplete.
Expend comes very close to spend in meaning, but it tends to be used more in reference to business, industry, finance, or government than in reference to private persons and therefore to imply larger sums or more determinate ends.
In its extended use, too, expend tends to imply largeness of outgo and often, like spend, suggests a depleting or exhausting of what is being used, but it not infrequently carries an added suggestion of futility that is not apparent in spend .
Disburse basically implies the paying out of money (as from public revenues, a huge fortune, an institutional income, or a society’s funds), but it also may imply distribution (as to pensioners or among heirs) and often stresses an acting under authority in such paying or distributing.
When extended to nonmonetary matters, disburse is likely to stress distribution.