I actually think it should be half the strength of a shrine as according to the wiki, a shrine can be more powerful than an inexperienced priest, and it seems like if you become a priest you should be doing more converting off the start than you did with your unit. Also the prices should be higher, especially if you allow more than one religious paraphernalia, as shrines are quite expensive for the priest, so should it for the "mobile shrine," so it would be something like 50 to buy and 5 a week for the first one.
