IMHO, I would absolutely need a rotary cutter and mat, because I simply will not be able to accurately cut squares and strips. A 24x36 inch mat is on sale at JAF for $30 right now, and a Fiskars 45 mm cutter is $9. I'd buy a 12.5x12.5 inch ruler so I could square up my blocks - $17. And I'd probably get a longer ruler for cutting strips - $12. Without taking any coupons into account, that'd be $68 for things that didn't include the fabric, batting, or thread. (I'm assuming that if you have a machine, you also have an iron, ironing board, and basic fabric scissors.)
While I have plenty more stuff than that, I'd say those are my bare minimums. YMMV