We used 2 pairs of the Motorola T4500 for a recent trip to Tokyo. I think I bought them for about S$55 (grey set, no warranty) in Sim Lim Square. If I remembered right, Funan was selling them for about S$75.
It is really small and handy. However, the clip is awful. We must have dropped each set at least half a dozen times. Better to chain it around your neck. At least they are all still working.
It uses 3AAA batteries. When fully charged, rechargable AAA batteries (not provided) lasts about 2 days. The effective range is about 1/2-2/3 the width of Tokyo Disneyland. In Tokyo, the maximum range was about 3 blocks. It will cover a small shopping center easily. We used 3G phones for backup when the walkie talkies were out of range.
The more powerful models that cover 5 miles are much bigger and more expensive but comes with rechargable batteries and gives you the option of adding an earpiece. Which model to get depends on how far you intend to stray from your partner, I guess.