Final Cut exporting significantly worse quality video regardless of settings/format.

I'm having a problem which may or may not have been plaguing my small studio since day one. Every video that we edit in Final Cut Pro exports in MUCH lower quality than it was when it was imported, not only that, the file size of the newly exported video is several times the size of the original. What I end up getting is a file too large for our clients to email around. We recently had a client come into our studio with a flash drive full of 15 second avi's no larger than 900 KB, he wanted a few of them edited together with simple cross fade transitions, and even a few seconds of dead space cut out. He needed them to be the highest quality possible for a powerpoint presentation he may now be unable to give. At first I exported them as Uncompressed avi's, best quality, thousands of colors, and no sound. The resulting file was not only blurrier, but now 260.5 MB!! And that one was with zero edits! The original was 803 KB and crystal clear. So after that I decided to try a few tests. We also produce a bi-weekly hour-long local television show, which looks fine on television but now I'm wondering how much better it could and should look. I've been exporting that out as a Quicktime, Apple ProRes 442 HQ, Interlaced bottom-field-first, zero filters, both compressor native and NTSC 720 X 480. I attempted this method on the client's original 803 KB with zero edits and not only did it export a completely unusable video compared to the original, but it was now 57.1 MB. What is going on here? Is Final Cut conspiring against me?

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This was after I created a new project, made the sequence settings into Apple ProRes lt 30p under the audio/video settings in Final Cut, and exported it as the same with 'current' dimensions (it was listed as 850X637, maybe that was the original?) Although I did have to render the original avi itself once it was placed in the timeline which you shouldn't have to do if the setting is the same as the clip. I guess there's no way to know exactly what sort of avi my original file is so I can match my sequence to it? The 'more info' (to be fair im sort of used to 'properties') leaves something to be desired..
Thanks everyone.

I am not sure how sophisticated you need to get for your videos, but if it is simple edits, I would recommend Windows Movie Maker. It is a free download on your PC and I have never had any issues with creating movies, transferrring, burning, or losing quality. It is extremenly easy and intutitive to use. I recently have been trying to do more sophisticated editing using Mac's Final Cut Pro and it has been one conundrum (sometimes it feels like a "conspiracy") after another.

I need to get quite sophisticated in my videos, as I work at a small television studio with two older gentlemen more accustomed to shooting talk shows in standard definition than editing video. We shoot several hour long tv shows that usually showcase local businesses, as well as commercials. I am still able to produce such work, though I feel like the videos should be of exponentially better quality than what they are now.

I do know that AVI's are not optimal for editing in Final Cut. They need to be converted to a Quicktime format compatible with FCP BEFORE importing them, not just exported to one. Also, AVI is a container for several codecs, so results may vary and files sizes may be bigger to compensate for limitations of the original codec.

I would try converting the AVI footage with MPEG Streamclip or even export it to a QT codec from Quicktime Player. Maybe someone else can give you specific settings.