HOA stands for Homeowners Association. The amount is determined by the HOA itself in conjunction with management company overseeing the HOA and it's based on the budget required to both operate the development as well as to fund the capital reserve.
I can tell by your question that you should absolutely be working with a Buyer Broker. This won't cost you anything and will likely save you money and time. They will be a great source of information which you'll both need and want.
If you're looking at condos or townhomes you cannot avoid an HOA fee, as you don't own the outside of the building, this is owned by the HOA. If you're looking at single family homes you can avoid HOA fees, simply don't buy in an Association.
HOA fees can cover a wide variety of things, amenities such as pools, gyms, tennis courts, etc., maintenance of the exterior of the building (condos/townhomes) maintenance of the grounds, common area insurance, etc. Each HOA is different so there's no way anyone can answer your question specifically without knowing the exact development you're looking at. Most HOA determine the exact fee based on the size of the unit not the price paid, unless their all the same size in which case the fees are identical for everyone.
Do yourself a huge favor , read the link I've attached below and then start interviewing local agents to find yourself an experienced buyer broker, you'll be glad you did.