Assuming these two websites have their own domain names, and they are all in the commercial usage. Thus, you want to encrypt the data for your customers.
Situation one, the minimum cost is my world!
Go get DC SSL * 2 for your websites, some vendors provide cheap SSL for as low as $5/year.
Situation two, brand reputation is my heart!
Go get EV SSL * 2, a green bar gives you a sugar bar due to most people regards the green bar as the better encryption and product guarantee evidence (EV verify the address and the business document of your business)
The cost for two EV per year is at least $500
Situation three, get a balance between cost and brand!
Go get UCC SSL which allows you to create at least 10 different domains (differed by vendors) in one certificate,
avg price is $120/yr for one UCC.
However, if you build two websites to compete with each other for the same good, then you shouldn't get the UCC due to smart customers can easily find out what domains are protected by this certificate.
REMEMBER,
The brand of SSL certificate doesn't indicate the data encryption level !!!
You need to set the ciphers yourself.