Invasive plant on property we are due to purchase

[Mentalblip]

So, we put an offer in on a property last winter. Been to see it 4x since and got a survey. Turns out there’s a load of bamboo (much more than first met the eye) so commissioned a proper bamboo survey.
This revealed over 130sq m of bamboo of the running/spreading variety with significant spread into one neighbours garden and minor but definite spread to another neighbours garden. It’s over 20m from any property thankfully.
quote well into a 5 figure sum for killing it with herbicide (all gardens to prevent it respreading) and then removing it (our garden to be).
Wwyd? Try to renegotiate? Run?
Words of wisdom appreciated 

Vendor isn't budging :( sighhhh

@Mentalblip probably time to walk, or maybe run, from that property.
The vendor will continue to have problems selling but that’s their problem.

Time to walk if they won’t budge.