Hmm, that's kind of an open-ended question... are you actually asking about the "cost" of a Belgian Hi Power? If you are collector looking for a specific model of the Hi Power, like the Capitan, then you may value it quite highly (and be willing to pay a higher cost), especially if it is in good condition. If you are looking for a shooter, then whether it is a Capitan, a Mark III, a clone, or whatever won't mean so much, some wear and tear won't matter as much, and you probably can pay less.
Having said all that, when I have taken notice, most new FN-produced, Browning-marked Hi Powers seem to be at least $800+, and higher. Older models may go for more or less, depending on their scarcity/desirability/collectibility. There isn't just one model or version of the HP, there are different generations (e.g. "classic," Mark II, Mark III), pre-, during, and post-WW II models, target shooting models, etc. Some have the Browning rollmark, some (like mine) have the FN marking.
Try Mr Stephen Camp's section on this website, and/or go to his own website (
http://www.hipowersandhandguns.com/" onclick="window.open(this.href);return false;), and he and a lot of Hi Power aficianados hang out at this forum:
http://handgunsandammo.proboards36.com" onclick="window.open(this.href);return false;
I bought two FN Hi Power's for between $400 and $500 a couple years ago. I have not seen those prices since, and don't expect to again.
Good luck.