@alexsh1 Happy to been helpful:) But, remember if you want to apply a PIR sensor in instrumentation, you have to use lithium tantalate pyroelectric detector rather than simple ceramic one. Ask me before.

@alexsh1 Why do you need a 50 euro demonstrator? A PIR sensor has 3 outputs: +, output, common. There is a 47K resistor between output and common. The circuit of an alarm sensor is very simple. Next, you can either make an alarm sensor using a circuit for example taken from here

http://unhas.ac.id/tahir/BAHAN-KULIAH/ELIN/NEW/AlarmSensorandSecurityCircuitCookbook.pdf

page 230 (you can use any ceramic PIR sensor instead of Model 5192 on lithium tantalate described by the author), or connect it directly to an A/D converter, and "play digits".

You can order good quality dual ceramic PIR sensors at kube.ch or
http://www.excelitas.com/Pages/Product/Pyroelectric-Detectors-and-Sensors.aspx
Remember that no name manufacturers give no name quality.

Want to know more about how PIR sensors work? Feel free to ask me.
https://sites.google.com/site/pyrodetector/
If I am skilled (if your question relates to a PIR sensor itself), I will help. Otherwise, I may try to help you, at least, by saying what I think about your problem. Good luck:)

@TheoL kube.ch produce high-quality ceramic PIR sensors. They cost less than 10 euro. They work well (I develop and sell simulators for PIR sensors from $1 to ... . I know principle of operating) Just, use good sensors and forget of problems. Cheap sensors give cheap quality. If you want a lithium tantalate single crystal PIR sensor for instrumentation, go to silverlight.ch Be ready to pay $150, but you will get a "porshe" PIR. I have samples from these manufacturers. LT sensors for instruments are magic! There are a number of other manufacturers, but most of them don't sell their products to private persons (reasons are obvious)

"what is the best pir sensor with an affordable price" that can be used for DIY
If you want to do a thing by yourself, with a PIR sensor being cheap, you had better choose a PIR sensor from this manufacturer
http://kube.ch/pyroelectric/index.php
Read how they test their PIR sensors under humid environmental conditions
http://kube.ch/downloads/pdf/kube_sensors_stability.pdf
If a sensor is extremely cheap and is not sealed properly, moisture when comes in, just short-circuit the high-megohm pyroelectric sensitive element. No need to explain further...
You can buy a high-quality ceramic PIR sensor from KUBE for less than 10 euro. Lower price (10 euro for a bag full of PIR sensors) will give the low quality. You will be upset from the low quality longer than happy from the low price.

Hello.
It is not a question which PIR sensor is the best. The question is that who will sell it to you? There are a number of manufacturers which produce high-end pyroelectric detectors, but they don't sell them to private persons. Good quality lithium tantalate pyroelectric detector which you can use in instrumentation, costs approximately from 150 to 500 USD, and even higher. I know one supplier who sells their products worldwide. That is

http://silverlight.ch/order_detectors.php

Choose the last detector Model 446M2-3 and you will be happy. This is a "BMW" pyroelectric detector. If you have a bag of money, you, probably, can order "BMW" detectors from these people

http://www.scitec.uk.com/infrared_detectors/irsensors_ordering.php?Submit1=Buy+Now

In general, lithium tantalate pyroelectric detectors are not sold to private persons. Mouser, Farnell, and other distributors do not sell such things. They can sell only cheap detectors based on ceramics that are unable to be used in instrumentation.

If you have questions about pyroelectric detectors, I may try to help you. Contact me at

https://sites.google.com/site/pyrodetector/

My research relates to mathematical modelling of pyroelectric detectors. I develop simulators for "BMW" detectors.
I hope, this helps.
Kind regards.