Low end heart rate monitor

Timex makes a few sub-$100 watches with HRM.  http://www.timex.com

I've had great luck with Sigma Sport PC-14.  Now discontinued but the newer low-end models seem solid as well.  Although I have a Garmin 305, I find I use my "low-end" PC14 just as much.  I'm not doing elite training, so mean and peak HR along with route, speed, & weather (temp/wind) give me a decent log of training intensity for each session.

I have a Timex system and it works great for me.

you can find a garmin 305 online for about 125$. A cheap one is going to be near to 100. If it has a strap. That is what I would go with. Later you can expand by getting a cadence/speed sensor and a foot pod for those gym running days. 

This is what I was thinking as well.   The 305 is an awesome training tool.

x2

The Sigma has gotten me through 2 years of training now for around $35 bucks.  Laps, avg hr, max hr and you can set one training zone.  It's plenty for what I do.

I would avoid those DIGITALLY CODED heart rate monitors like the plague They use the same frequency 2.4ghz as 3G phones. I dont want that near my heart! I stick to analogue heart rate monitors is my advice.