Shri RAma: 110+/- years
दशवर्षसहस्राणि दशवर्षशतानि च । रामो राज्यमुपासित्वा ब्रह्मलोकं प्रयास्यति ।। [source]
After serving the kingdom for several decades and ten years after [the age of] hundred, RAma proceeded towards Brahmaloka (highest of all planes).
Refer this answer for more anaylsis.
Shri Krishna: around 80 years
In Mahabharata's trusted edition, I could find only Drona (85) & Abhimanyu's (16) ages at war time. And based on Gandhari's curse of 36 years, we can infer all the other characters' ages.
If Bhishma was 85-90 years, then Yudhishtira would have been at least 40 years younger to him. Which makes him 45+/- years and hence Krishna & Arjuna around 43+/- years. After 36 years, Krishna died during Yadavas' civil war, hence his age would likely be less than 80.
Refer this answer for scriptural based analysis.
Additional verse: In Shrimad Bhagavatam 11.6.25, there is a following verse:
yadu-vaṁśe ’vatīrṇasya bhavataḥ puruṣottama śarac-chataṁ vyatīyāya pañca-viṁśādhikaṁ prabho
Now they have translated as "hundred and twenty five years". However it can also be interpreted as following, if done word by word:
The best among the men, who descended in Yadu dynasty; O lord you would live hundred autumns, after passing twenty five more [years].
Which means Krishna was at the age of 75 years, when this was said. Had he passed 25 autumns more, he would have finished 100 years. In Sanskrit, a sentence can often be interpreted in more than 1 ways. Also, it matches with the Mahabharata based age of Krishna of <80 years, as mentioned in the linked answer.
Lord Kalki: Unspecified
Kalki is a futuristic avatAra and there are lots of stories around him. MahabhArata mentions that, he will be born during beginning of next Satyuga. Nothing much about life span.