气力 emphasizes the bodily/internal energy spent on a task — close to 'effort' or 'wherewithal'. Compare
力气 (lìqi, the same characters reversed!), which is more often raw muscle strength:
他力气大 'he is strong'.
费力气 and
费气力 both work for 'take a lot of effort', but
气力 has a slightly more literary feel.
