Sorry I was in a meeting, it always seems that my day job gets in the way of good questions.
Without Pro you cannot use the batch sequencer, as you rightly point out. You said:
"So I am thinking I have to purchase a tool or something, but I can't do that"
What do you mean " I can't do that"?
I am not aware of free or lo-cost option of Batch processing tools that work on Doc Properties level, there are many PDF converters but not with that functionality.
Your best option is to upgrade to Pro as it will be the most reliable tool for you given that you work with a large number of files and upgrade costs should be cheaper than doing all this manually.
hth
capt.