Are you sure that it necessarily has to be an ad? Perhaps you can find a cheaper alternative to draw the attention of your target audience to your company?
In daily newspapers there are usually not many ads (that means little competition for you), because ads are very expensive. Ads in advertising newspapers on the other hand, are slightly cheaper, but you have much more competition as they are cluttered with ads. Thus, your ad will drown instead of drawing attention. Moreover, it is questionable if you can reach your target audience with an ad in a newspaper. Only if you are absolutely sure that the readership of the newspaper accurately reflects your target audience, you should place an ad.
A cheaper alternative to ads in newspapers are ads in local and official gazettes. These also have the advantage of being read, as important information for all citizens of the city can be found here.
If you offer your products / services for a very specific audience, I recommend ads in relevant journals. However, you should offer your products / services nationwide, as journals do not have regional or local editions.
Ads in popular magazines tend to have a high circulation. Thus, prices for ads are also extremely high. However, you will reach a very large number of readers. Whether these readers are your target audience is questionable.
Other magazines that might be helpful for your ad campaign are city magazines, as well as student newspapers. Since the circulation is very small, ads are cheap. If readers of the magazine match your target audience, you should seize the opportunity advertise here.
In order to have success with your ad, you should only advertise in a certain time frame – advertise six times in a row. Only with repetitions your audience will notice your ad.
The size of your ad is irrelevant. Instead of advertising with a rather large ad, rather advertise with small ads that you can repeat more often for the same amount of money.
Have your ad designed in black and white design - this saves money. Of course, color ads are more beautiful, but all the other ads are in color too. Your ad will stand out much more if you keep it in black and white.