Google Adwords does not allow setting a max spend limit for the month.
Google Adwords allows a Daily budget for each Campaign. The automatic payment will be processed after 30 days, or the day you reach your payment threshold, whichever comes first. The payment threshold is $500. If your budget is $15 dollars a day that should equate to $500 per month.
If you are running 2 campaigns, each at $15 per day, then the Total Daily budget of $30 per day.
The budget can be paused or changed at any time.
Conversion cost is the cost amount divided by the number of conversions. The conversion cost is not the same as your daily ad spend budget.
All reports will appear in the Report section of the CRM. You can also view real time visitor traffic data using the visitor traffic software.
From Google Adwords Help:
Why costs might exceed your average daily budget
AdWords helps you maximize your return on investment (ROI) by showing your ads more often on days when Search traffic is higher.
When your ads are shown more often, your total daily cost might be up to 2 times your average daily budget, unless you're paying for conversions. If you pay for conversions, your daily costs may be more than 2 times your daily budget. However, with all AdWords campaigns you won't be charged more than your average daily budget multiplied by the average number of days in a month (30.4).
Why campaigns might cost more than their daily budget
For each of your ad campaigns, you'll set a daily budget — the amount that you've budgeted to spend on your ads each day. If you've noticed that the total daily cost of your campaign is more than your daily budget amount, that means your campaign is spending more of your budget on days with higher Search traffic and less on days with lower traffic. Search traffic can fluctuate for several reasons: whether it's the weekend or weekday, or due to seasonality and holidays.
Dipping into your daily budget for other days in the month helps to optimize the performance of your campaigns and helps make sure that your ads can run a little more on days when they’re very popular.
How you’re charged when campaigns exceed their daily budget
Up to 2 times your campaign's daily budget can be used to show your ads on certain days of the week or certain times of the month based on fluctuations in traffic — but not more than you spend on your campaigns each month. For campaigns where you pay for conversions, your daily costs may exceed 2 times your daily budget.
If your daily budget is US$10, up to US$20 can be used to show your ads on certain days based on fluctuations in traffic.
Note that sometimes your daily costs might exceed the cap of 2 times your daily budget. However, you'll still only be charged up to 2 times your daily budget. For example, if your daily budget is US$10, and you've accumulated $23 in costs on a given day, you'll only be charged $20 per day. The remaining $3 is returned to you as an overdelivery credit, which you can see in your transaction history.
About the monthly charging limit
While the cost of your campaign can be up to 2 times your average daily budget on any given day, you won't be charged more than the monthly charging limit that AdWords uses to prevent you from accidentally getting overcharged. This means that as long as your budget is consistent for an entire month, you won't be charged more than your daily budget multiplied by the average number of days in a month, which is 30.4 (365 days in a year ÷ 12 months).
If your budget is the same value throughout a month, and you accrue more costs in a calendar month than your monthly limit allows, you'll only be charged your monthly limit. For instance, if your daily budget is $10 per day throughout a month (a $304 monthly charging limit), and you've accrued $310 in costs over a calendar month, you'll only be charged $304. Here's the math:
US$10 (daily budget) x 30.4 (average days per month) = US$304
The other $6 is returned to you as an overdelivery credit.
How budget changes affect the monthly charging limit
When you change your budget, your spend for the rest of the month won’t exceed your new average daily budget multiplied by the remaining days in the month.
For example, let’s say you have a daily budget of US$5, and as of November 24 you’ve spent US$113. On the same day, you change your daily budget to US$10. The maximum you’ll be charged for the month of November will be:
$113 spent so far + ($10/day X 7 days remaining) = $183