Andrey, one way around the minimum charges/threshold is to get someone in the UK to buy for you and re-post what you're after.

I did this for a US member a couple of years ago, because the company's (not Silverprint) minimum order size & the postage charge was excessively high to the US, the actual postage cost was minimal even with the insured & tracked option (less than $5).

Alternately try and make a group purchase with some other Bulgarian photographers.

I'd be happy to help you when I'm next in the UK.

Ian