A calculation of current max pay rate:
There are 360 blocks per hour. The delegate gets 1/101 of these, and thus creates 3.564 blocks per hour.
Each time they create a block they get 50 BTS. Therefore they get 178.2 BTS per hour.
178.2 * 24 hour/day * 30 day/month = 128300 BTS per month for a full pay delegate.
Current prices are around .105 CNY per BTS, or about 1.71 cents.
128300 * .0171 = $2194 a month.
So around 2200 bucks a month for a full pay delegate at current prices of BTS, on the most liquid market.
Your 700 number is way off.