Framing can be expensive and it's the kind of thing that — with a little DIY — you can generally save yourself quite a bit of coin on. However, materials — namely good moulding — can be hard to come by. I've made frames myself from scratch, but when you factor in the time to source the wood and make the required cuts, rebates, and dados, it's hardly worth it.
We've purchased framing supplies from Metroframe.com for many years (since we were in West Oakland, so it must be nearly 10 years now... yikes). They sell a good amount of high-quality wood mouldings and — if sourced wisely — can save some money, specifically on shipping. One of their options for joining is "wedge joining" which used these ingenious little plastic wedges to hold the frames edges together. The bonus here is that you can join them yourself and save lots on shipping and packing costs — shipping a large frame (30X40, perhaps)‚ can cost as much as the frame itself, but shipping un-joined pieces is quite cost-effective. They also sell strainers, which is a pro-way of keeping the artwork in the frame as well as spacers and other framing needs. Purchasing glass or plexi from them isn't necessarily economical based on the shipping notion above, but I think 75% of the art in our house is framed with one of their mouldings. We'll generally head to a glass shop or TAP plastics for glazing.