Is $20,000 to waterproof a basement cold room from the exterior a fair price?

Water is leaking from the gap between the stone veneer and porch slab into the cold room of my basement. I was told by two sources that it's impossible to waterproof from the outside unless the entire porch deck is removed and replaced. My neighbor already extended the downspout near my cold room vent, but there still seems to be water leakage earlier in the year when the rain was heavy. I'm wondering if the more expensive exterior solution is worth it, as I know exterior waterproofing is real waterproofing, but it seems like I need to replace my front porch which will cost me way more. RCC Waterproofing assured me that the damage from the interior solution could potentially be many decades away.