The Valence are good batteries in the right conditions, but they are all used at this point. Yes you can generally get them cheap-ish (~$200?), but hard to say how they have been treated. I have had a few of the smaller RT series with BMS and none of them capacity tested anywhere near rating...
Your Valence XP does not have a BMS so you should not expect any protection that a BMS would provide such as low/high voltage cutoff, low temp charge cutoff, cell temp monitoring, etc.