How/Can we negotiate to lower the purchasing price after it’s already in Escrow?

[Moss Siridajnawanan]

We got out first BRRR deal a few weeks ago and it's still in escrow. We found out that costs of rehab is quite over our budget. We offered at $399,000. Rehab is $36,000 and ARV is $510,000. We are comfortable and expected to leave $50,000 into this deal but it turns out to be over $70,000. We still have appraisal and loan contingencies. Questions for you are

1. - Can we ask the agent to lower the purchasing price? 
2. - What kind of reason or how would the conversation be like?
3. - How can we submit the appraisal since my lender doesn't do current market value? We only have ARV report which is $510,000.