If you separate the monitor out, you can use $20 off $100 on the monitor, and $30 off $150 for the rest of the items + an extra $5. So, you use $55 worth of coupons, instead of $45.
But I can't get the $30 coupon and the $5 off modem coupon to work together, even when I put $155 worth of items in the cart...
Edit: The "General" $ off coupons (like $30 off $150) determine their min amount by the total $ cost of items for which there are no specific $ off coupons. So, you can't use the modem to get both $5 off and $30 off.
Still, forego the $5 coupon and do two orders for a $5 hotter deal.
Or: Add another $30 item to your cart, use both $30 and $5 coupons, then return the $30 item to your local staples. If they don't know the "No couponed item shall apply towards minimum for general couponage" rule, which IS fairly obscure, and the coupon codes don't exactly say what they're used for, you'll get to use both coupons..
-Alex