Is Percona xtrabackup the right choice for my 500GB MySQL backup?

Question

I have a MySQL db with 500GB, consisting mainly of Innodb tables, and one big (200GB) MyISAM table. My current backup strategy is copying the db files to an external harddrive. This causes a downtime of ~4hrs. My Needs:

1. Low cost.
2. Recovery time can be long. No need of real-time replication.
3. Can handle loss of data in ranges of 1week-2weeks.
4. Would prefer a short as possible down-time for backup, but can live with anything up to 2hrs.

Currently considering trying to move to Percona xtrabackup. Is it the right solution for my use case? I'm specifically concerned that it locks the MyISAM table and learning curve.