While the EX500 is a good beginner bike, I would check online yourself for these parts to know what they will cost. AND I would insist on an agreed price of the bike WITH the parts installed so you can hear it run and have a friend who rides take it for a short spin BEFORE you buy it. With a bike that old, you want to make sure it isn't damaged and runs OK before you exchange money.
The bike should be between $600 and $1400 if it's in good shape and running. I have a friend with a 1996 250cc Ninja for sale right now in decent running condition and he is only asking $1400 for it. That's 8 years newer than the one you're looking at.
If you want to gamble on it as is, I would only offer $200-$500.
Good luck and I hope you will be a proud bike owner soon.