If you play through the game and collect everything you should be able to buy everything from the supply shack. I beat the game and still needed 40 more gold coins to buy my last item.
What you want to do is go to previous Tombs and search around to see if you find any coins that you might have missed going their the first time. I went to 3 different tombs and was able to get the 40 missing coins I needed.
The Tombs are:Ancient Cistern
Voice of God
The Red Mine
House of the Afflicted
Catacomb of Sacred Waters
Baths of Kitezh
Chamber of Exorcism
Pit of Judgement
Here is a video of some of the coin locations I found: