Modelling conventions are a chance to learn about the industry, connect with the people that make things happen, and possibly be discovered.
These conventions are different from what scouting services offer in that they are packed with information, and offer a great chance to be seen by the scouts in attendance.
Generally these conventions last four or five days and give the contestants a chance to attend workshops with people that live and breathe modelling, as well as attend a number of seminars on modelling essentials.
Various competitions are held, which further give the contestant exposure to the international panel.
Although the cost to attend these conventions is higher than the price of a typical scouting service, the information, exposure and opportunity to interact with the industry professionals makes up the difference.
In North America you can expect to find such competitions as commercial print, swimsuit, photography, runway, and covergirl/coverman. Most of the conventions also have a talent portion which includes categories like T.V. Commercial, Monologue, Improv, and Cold Read.
Costs vary greatly between conventions, as does the number of contestants.
Most models attending conventions, do so under the umbrella of their mother agency. Many agencies use conventions as a way not only to promote their models, but to learn about new trends in the industry.
One thing to be aware of is that many agencies use conventions as a way to generate additional funds. It isn't uncommon for agencies to sell "convention packages" which include additional classes to prepare models for the convention. They may also include photos shoots, cost of travel and any number of other things to get the model ready for the convention. As with everything we preach on this site, ask a lot of questions before committing to anything.
Many conventions will not discuss costs with models. Organizing a convention is a large task, and most don't have time to answer indivual queries. It is also in the best interest of the conventions to respect the schools and agencies that support them.