Your online budget is the most important question to answer, you know how much money you have available for advertising and I fully understand the stress that can be caused from wondering where to spend it to ensure that you see a return on any advertising investment.
The majority of sites will claim to offer effective advertising, or give the impression through their site content that this is the case, which you need to accept (not necessarily believe) as, like you, they are in business too, and need to entice your custom.
Set your advertising budget and stick to it! You can always review and increase/decrease your budget at a later date. In my opinion, the only people that think that an advertising budget should be fluid are advertising sales people! I’m sure you’ve all met them – “I appreciate you have a budget, however if I could prove to you that …… “ etc. etc…
Budgets are important and budgets do matter so choose an advertising spend you are comfortable with and stick to it. Be aware however that by making this decision, your budget may exclude you from advertising with some online websites that are maybe outside your set budget. Such is life, your budget will always dictate your exposure.