According to here and here it’s $40 though the price may have gone up.

I found a website I won’t link to slinging pics of signed 155s for $200, but I’m not sure I trust the veracity.

We are grateful for your support to Ukraine through donations to other funds and NGO’s but we can’t accept them as proof of payment, because every donation we receive goes directly to the units we work with in the form of equipment, supplies, and other critical items. We work hard to cover the gaps left by the state procurement and supply chains.

You would think if they were real they’d take money for the war effort any way they can get it.

This would be a very easy way to scam people.