The suggestion of an FM transmitter from AKG looks pretty good. That extra power will come in handy. However, I'm not sure I would bother with the FM booster. Most FM receivers are reasonably sensitive enough already and you always get more performance boost by improving the receiving and/or transmitting antenna than you will by adding amplification at the receiver. In my opinion you would maximize your range by first making your transmitting and receiving antennas as efficient as possible, then by boosting your transmit power, then finally by boosting your receiver signal with an amplifier.
The type of transmitter you decide to use, whether that is a simple two transistor thing operating somewhere near 100 MHz (FM broadcast) or a VHF oscillator or whatever depends entirely on what kind of receiver you want to use. Since receivers are more difficult to get right than transmitters you should pick your receiver first. If it is to be an FM broadcast receiver, then that sets your frequency choice to around 100MHz. This is a good choice since it is easy to lay your hands on an FM receiver, and at 100MHz you can have reasonably good antenna performance in a small size.
You can choose any FM microphone circuit, such as the one recommended by AKG. This will be nice and small, won't take much battery power, and will be very light if you just construct it on a bit of perfboard (ie. don't bother putting it into a box or anything, just build it up and then put tape or a plastic bag around it). When you receive its signal on an FM receiver though, you will only hear a lack of background noise when the tx is on, which isn't a very positive signal to use. However, some FM receivers have signal strength meters that you can tap into for an on/off signal. Beware that such circuits usually don't respond very quickly, so it likely wont' be very good for RPM pulses. Otherwise, you might want to consider modulating the FM mic with an audio tone so that you have something to work with at the other end. Then, at the receiver, you would use a tone decoder or other simple circuit to change your audio tone back into a pulse stream.