Had almost this identical insulation situation when I bought my house. The ceiling just had some thin rock wool. First I went to Lowes and got a few cans of fire-rated spray foam and used it to seal around all ceiling fixtures, canister lights, wire penetrations, anything air can leak from. Next I built a little dam with scrap wood around the access hatch. Then spent one Saturday with a friend blowing insulation in. 8 hours of blower rental was free for every 3 bags of insulation you bought, but it didn't take nearly that much time. Had it up to R-48 depth in only about 4 hours of blowing. I submit the receipts to my state's energy rebate program and was 100% reimbursed. I think the blow-in did a much better job and was easier to get into odd shaped framing than bat would have been.

My winter gas bill halved, much better than I hoped. I also wasn't expecting for my summer AC to bill drop by almost 75%. My house was MUCH more comfortable too. Almost all the draftiness disappeared after that.

I paid $0 after rebates, spent probably 12 hours labor total, and save easily $100-$200 a month.