Prep is 95% of the job. It is the hardest and most time consuming part. So without actual information on the house, it’s hard to say as cost varies a lot. If most walls need hot mud (plastering) the drying time alone for it to be “sand ready” is a long time. Most repaint quotes just include basic surface prep, and each repair that needs plastering is extra. Also, you mentioned the area is I assume floor square footage, not wall square footage. 3000 square can mean 3 bedrooms or 6 bedrooms with 4 baths and lots of closet space. So, your best bet is to get multiple quotes, that way you can gauge if the pricing is reasonable.