I've run $350 + higher end AGM batteries. Even in the E53. Currently running a wet cell.

IMO, AGM is worth it if one deep discharges it (in this age of ED, AGM is a must). Or concerned about long term storage, discharge factor if not in a batter minder.

On the flipside, AGM is very sensitive as battery charging voltage and if you may have weird alt issues, those will reflect downstream on your battery whereas a Wet Cell can take some voltage burps. Just my 2 cents

Now that more vehicles demand AGM due to start-stop charging profile, AGM's have become a bit cheaper