What point were the Bnei Cheis making when they called him a prince of G-d and with the rest of their statement?
Rashi (in Yehoshua, 14:15): As a reward for calling Avraham "N'si Elokim', they merited forty years of peace whilst Hashem kept Yisrael in the desert.
Rashbam and Seforno: They were saying that since they considered him a 'prince of G-d', 1 he could bury his dead in the location where they buried the princes (or wherever he wished) 2 and did not need to wait till he purchased a burial plot. 3
Ramban: Refer to 23:8:1:1*.
Rashi also writes in Shabbos, 105a that, based on this Pasuk, the Gemara learns that Hashem appointed Avraham king of the nations - See the Gemara there.
Since nobody would withhold a burial plot from him.
As the Gemara states in Mo'ed Katan 22a - 'The quicker one buries one's dead the better'.
רש"י: לא יכלה...כמו לא תכלא רחמיך: כאן כתוב "יכלה" בה"א ושם כתוב "תכלא" באל"ף?
גור אריה: אותיות ה"א ואל"ף באות זו תחת זו.