There is a trend away from the expensive “in-house” AV equipment and service to AV companies that are local and still close to your event. The advantages of an “in-house” provider is that they are ON location and in the event that things go wrong, the theory would be that they can be responsive quickly. The down side to using these providers is that you will be charged a “surcharge” just like if you order room service at your hotel. Expect this surcharge to be in the 20% range.
Also, the “in-house” AV provider has to pay a percentage of your AV charge to the conference property management. This charge is typically between 25-50% of the AV charge. These charges are NOT a factor when you use an outside provider. In House AV Providers know that you are coming to their property and will call you to discuss your AV needs. Some of these companies may give the impression that you are obliged to use their expensive AV services. In the case where you have signed a contract that states that you HAVE to use In-House AV, that would be correct. However, you can let the conference space liaison (person that you are talking to about using conference space) that you are not willing to CONTRACT the in house AV unless and until you have explored your AV cost options.
A conference property wants to rent you hotel rooms, meals, drinks and conference space. Chances are, they will have no problem allowing you to bring in your own outside AV services.