The best thing to do is simply talk to the sellers, let them know the scenario. If the scenario seems fishy, they may not want to extend the contract. If they say no, talk to an attorney/agent for more advice.
Of course, if you are working with an agent, they will inform you of the best options for you.
I'm buying the home thrugh a realtor. We will be paying cash for it. I may or may not need 10 days but I think it would be smart for the owner to agree. If it were me $280,000 would be hard to pass up in cash!!!! If they won't extend it can we sign another contract and put more earnest money down?
Hopefully you're working with a Realtor. Have your Realtor ask the listing agent for an extension - explaining the reason(s). All parties will have to agree and sign the extension. If the seller doesn't want to extend the contract, they don't have to but in today's market, they may be willing to (depending on the reason for the extension).
You can ask, but you should have had the funds available when you wrote the offer unless this was disclosed up front. Most sellers in today's market will be accommodating. An addendum extending the closing date would be in order, but it is best to let the seller know immediately before they make financial decisions that could cause them harm.