Mine as well invest in good hardware, because it's generally always worth it. Try ebay, they have aluminum anodized ones. I've been using mine for years, they look great and you shed a little weight too. If you search you'll find a decent deal, but I don't think I payed much under $20 bucks to be honest.
Go to your local Fastenal with the size that you need. M4x20 fine thread by the sound of it. If you have one of the old bolts you can take it in there with you and theyll size it up exactly. You might have to buy a bag of like 20 or 50 or so, but it'll still be much cheaper than $20 a bolt. Like $10 for the whole bag probably. Go stainless steel route and tell them you're okay with paying 30% markup but nothing more. They can adjust the price from there and get you a great deal. The typical markup on stainless is somewhere around 150-200 percent. Everything else in the store is marked up around 25-30 percent as thats the industry standard.