This one too cheap?

Audio-Technica | ATR3350 Omnidirectional Condenser | ATR3350

Is this video for just in company viewing?
Is the talent going to be moving around a lot or stationary at a table?
Is there a lot of electrical equipment in use?

The AT mic uses an unprotected cord that could pick up electrical buzz or interference. If you just want a simple instructional video that explains how to preform a procedure and seeing is more than hearing than the mic will probably do what you need it to. If on the other hand you ever want to reproduce and distribute this video and audio is a vital part of the production you would want to look at a better mic. At about 30.00 its something that you could try and your not out a lot of money.

A local low budget broadcast station in the area uses equipment that sounds so bad I have to mute the TV to watch the instructional video because of the sound. I would rather read the text than listen to the noise.
It's the old adage that people will watch a poor picture but not listen to bad sound.

What about this one.

It looks like it needs to plug into something specific

Audio-Technica | AT829cW Cardioid Condenser Lavalier | AT829CW

What about this one.

Will my XLR phatom power help this one work?

Shure | SM11-CN - Lavalier Microphone | SM11-CN | B&H Photo Video

A $25 mic in the right place will sound better than a $2500 mic that is too far away (or aimed in the wrong direction, or inappropriate for the ambient).

You can go to Amazon and buy a Shure WH20XLR Headworn Cardioid Dynamic Microphone with XLR Connector and Detachable Belt Clip AND a 15-foot XLR mic cable for $83.76 Two of those fit well within your budget (even including shipping) and will give you far better results than your boom microphone.

Amazon.com: Shure WH20XLR Headworn Cardioid Dynamic Microphone with XLR Connector and Detachable Belt Clip.: Electronics

Greg, don't try to cheap out. You don't have to spend a fortune but when you talk about moving from shooting the family just for the fun of it into shooting video for business applications, you're moving into an area where quality matters. Thing of the audience, what they see in other business presentations and what level your video is going to be compared to and let that be your guide to the level you need to achieve.

The last presentation was done with a $100 VHS camcorder.

I am going to be leaps and bounds above...

But I do get your point... I normally don't buy cheap things that I use all of the time.

Maybe something like this?

MXL | FR-355K Lavalier Interview Microphone Kit | FR-355K | B&H

All the mics you linked to have issues, I think. Some have the wrong connectors, some have cables that are too short, and I think the headset mics just look weird for what you're trying to do.

But have a look at this page. If it were me I'd just pick the first one I found with XLR and a long cable. Actual audio quality is less important than just being able to physically get it close and making it work.

Lavalier

Thats good stuff!!
I can swing that.

Since I have never used a mic before, I suppose I should have a set of headphones to make sure the sound is good?

Amazon.com: Sennheiser HD590 Full Size Headphone: Electronics

I have these at home already, any reason why I should not use them?

Sony MDR7506 are the industry standards ... Sony | MDR-7506 Headphone | MDR-7506 | B&H Photo Video

The above Sony's are great for multitracking and recording live productions. They are a bit bright, so they cut though the clutter. I prefer the Sennheiser HD 280 Pro cans for accuracy. They don't cut as well as the 7506s, and don't have as sweet a sound, but I find them to be more neutral and accurate.

If you are monitoring on set, both will do, and you might prefer the Sonys. If you want to do a critical review of your recordings in a midnight studio setting (with sleeping kids), I'd get the Senns.

Of course, good monitors are the best for monitoring for many reasons. That said, headphones are a nice sanity check, and you can pick up a top pair for $100. Good studio monitors can easily cost ten or more times that. And to sound their best, you want an acoustically treated space.

YES absolutely! Recording audio without monitoring on headphones is like framing and focusing without looking at the vieiwfinder!

Your headphones are likely perfectly fine for the level of production you are doing now. If you continue doing in-house corporate productions, perhaps you can get some budget to beef up your equipment arsenal.

I think you guys missed the point that I already own a pair.
Sennheiser HD590 Full Size Headphone

One says buy Sony or a different model of Senn?

I am guessing what I have will be good enough

Yep. The HD590s will do the trick.