How to calculate how many sums of an increasing number fits into another number ?

The title may be a bit misleading but I dont know how to name it better.
Here is the issue: Im designing a game and I need to develop a formula for my excel.

I have a table with 3 different types of weapons. Each weapon has 5 upgrades and each upgrade costs certain gold which increases per upgrade.
For example: Sword 1 UPGRADE 1 costs 100 gold, upgrade 2 costs 200 gold etc.

Now to my issue: On column A, I have 20 levels player can play. On Column B, I have how much GOLD player has in that level.
On Column C, I need to calculate maximum upgrade of weapon player can afford at that level.

For example, at level 1 player has 500 gold. Therefore for sword 1 he can afford a maximum upgrade 2 (because 500-(100+200)).

I hope it makes sense, thanks for your help guys.