Offered mid-level PD role but was interviewed for Senior PD role

Hi I interviewed with a YC startup. Went through 4 round, including design assignment of their own product. They were hiring for senior PD role and their budget was let's say X.

They offered me a PD II role with 35% less of actual budget. They all liked my profile and interviewed me like a senior PD only. Should I accept this considering the market situation or should I negotiate and if they don't agree on my number, I should reject the offer?

Only 2-3 designers are there, very young team.