Let's put it this way, if each message takes up 1K (and it's probably much less than that on average), and you send or receive 1 message every minute you're awake (16 hours a day) for a whole month, you'd use 29 MB for those 28,800 messages, or less than 15% of even the smallest 200 MB data plan.
Yes, pictures are going to use more data. You could send 1,000 (about 33 per day) 100K picture messages (again, that's on the large size, most .jpg pics will be smaller) and only use 100 MB, or 50% of your 200 MB data plan.
Now if you're sending 30,000 text messages or 1,000 picture messages, it seems pretty obvious you aren't a good candidate for the "light user" 200 MB data plan anyway. Most people are going to have a 2 GB data limit. Under that, you could send your 30,000 text messages and your 1,000 picture messages and only use about 6.5% of your 2 GB data limit.