If the intended venue requires a frame or you don't like the look of a gallery wrap (I think they often make a painting look cheap - Like the artist is saying -This painting isn't worth the cost and effort of providing a frame.) there are less costly alternatives to having custom frames made.
If you decide to frame it, I would suggest starting out with a pre-cut frame ordered online, that you assemble yourself. The shipping will be less expensive since it can go in a tube rather than a huge 3x4 foot box and you will save a ton of money over a local frame shop. What I often do is use the same frame over and over with different paintings in it for shows and gallery sales. That way if it doesn't sell I can put another painting in it. If it sells, GREAT! - I can order another frame.
Here is one example of a metal floater frame that you assemble yourself. With some searching, you might find something you like for less money.
If you already have the tools and the skills, making your own frame from moulding or lumber is going to be the lowest cost but it is not an easy task for someone who has not worked with wood, to cut and assemble their own frame..