Older shows like the Hellsing TV series always have various versions going in and out of print, meaning that prices fluctuate wildly. Hellsing TV in particular was distributed by the now-defunct Geneon and went out of print when that company folded, which would go a long way toward explaining why its price has been artificially inflated. (Funimation rescued the new Ultimate Hellsing OVAs, but not the old TV show, so as far as I know it's currently effectively unlicensed.) Prices were rock-bottom right after Geneon crashed when they were trying to get rid of their back stock, but it looks like they're back up again.
Your best bet for finding a good price is probably to keep your eyes open for used copies of the single-disc version rather than try to track down the full series all at once. It'll take more work, but it'll be a lot cheaper: Amazon Marketplace currently lists them at around three bucks a pop used, meaning you'll probably pay under $20 for the whole deal after shipping. I always see them at my local Bookmans for very reasonable prices, too.
Like Soundmonkey said, just keep a close eye on the customer approval rating when buying from Amazon Marketplace. Personally I wouldn't go under 95% if I could help it, but that's just me. The nice thing about buying from Amazon Marketplace as opposed to eBay or wherever is that you have someone to complain to if the seller screws you over, so most of them will accept a return for a refund if you get unlucky and get shipped a bootleg.