Purchase vs licence is an interesting decision.
Here is what I am thinking about,

If you are,
1. with strong financial position
2. with qualified R&D team which could continue to pursue further development
3. with the intention to nurture a strategic competitive edge
then
you'd better purchase the patent

IF not, you may consider get a licence to use the technology.
The method may not be cost efficient in the long run, (like installment purchase)
however may be a wise investment in the short term.

thanks  for your suggestions!