I went to Poland for the initial medical, it was 600 zloty in Warsaw and £50 for flights. With Hotel, food and few beers it cost me around £300 all in. I figured if I fail the medical it hasn't cost me too much and I've had a jolly to Warsaw.
It was cheap but the language barrier is a big issue and the facilities are old. It was very busy with military students and there is a queuing system in place for each exam. Pilots have priority over students and are seen to quicker than everyone else although I didn't know this because I don't speak Polish. I met a Ryanair captain who was there for a medical and he translated a lot for me. Had it not been for him the experience would not have been enjoyable.
I've since transferred my medical records to the UK which cost another £77. However, the Polish CAA cut my name out of my ECG trace before they sent it which meant I had to get another trace done by an AME at a cost of £75.
The SOLI was a ball ache too.
Best advice is to do it in the country you intend to issue your license, oh and get it done before you invest in flight training.