The seller just purchased the property 1 year ago for 5.8m and I would be paying in the mid 7m range which is a tough pill to swallow.

You may be able to get a prescriptive easement, which can give you the right to use that land permanently.

Option 2: The Close your Eyes and Wait Act1 - Tell them there's more where they came from, and if they want to eliminate them they should call an exterminator.2 - The cost of the exterminator is not the landlord's responsibility...of course they wouldn't be able to get past the laughing on the other end of their call to the exterminator to worry about any arguments about the cost, and who pays for it.Option 3: The Placebo Act1 - Buy a supply of aspirin (not for you, although you may want to keep some).2 - Put them in a bottle labeled Anti Spider Pills3 - Tell them to save the next spider(s) they kill.4 - Give the bottle to them and tell them to crush the pills. 5 - Mix the crushed pills with the crushed spider and spread them throughout the house.6 - Tell them this works, but only if they do this often since it depends on the quantity of spiders they use...the more the better.This last one should at least keep them busy for a while, and you will have a free "spiders be gone" service.

One of the guests at the pill party. 

Is the seller doing anything illegal here or do I just have to swallow that pill and move on??

(It certainly wouldn’t make sense financially for you not to do that.)I know “cash-for-keys” can be a hard pill to swallow.

It is a year round process, not a few magic pills on 12/31

Sateen have a tendency to pill up.

Swallowed the hard pill and sold my dream car , cut off time wasting hobbies, bought books, listen to seminars, observed the greatest Real estate investors across the country and began DOING IT! 

So this is a bitter pill to swallow at these prices.