SFDC/MKTO Duplicate Records (Best Way to Dedup)

So, after a year and a half, we finally connected our CRM to Marketo (I know, I know ... late). While we were waiting to get these connected, we've been uploading lists from SFDC into Marketo in order to send emails. Just this past week, we were able to get our CRM hooked up (yay) but now we have thousands and thousands of duplicate records. Email is the same, but we want to match up the MKTO record to the SFDC record.

Questions:

1. We do not have the budget for a paid solution, so are there other methods we could that would work in this case?

2. One of our partitions hasn't been filled. Is there something we can append the SFDC record before syncing that would make Marketo go "oh, I know who you're reaching to ... I'll magically match that for you."

I just find it strange that there's no simple-ish solution for the dups, or a rule that I could say "take lead score but update all the other data with what SFDC brings over."

Any help would be greatly appreciated. We really don't want to manually go through thousands of records one by one.

Thanks!