Building a wireless sensor network won't be very cheap but it can be loads of fun.
This is one approach to an Arduino based wireless network:
For a wireless sensor you probably want a temp sensor like the DS18B20.
You need a microcontroller (Arduino) that can read the values from the sensor and you need a wireless transmitter to send the sensor readings to your "hub".
The cheapest wireless transmitters and receivers around seems to be the OOK 433 units on the page you linked. They are apparently out of stock where you were looking but they are available from other sources at lower prices.
I've bought them from eBay and yesterday someone here recommended ElectroDragon (http://www.electrodragon.com/?product_cat=wireless-modules
You might need an Arduino and a transmitter for each sensor. If some sensors are closer together they could share the same Arduino/transmitter.
You will only need one receiver for the hub that will collect the data from your sensors.
This will soon add up to a lot of Arduinos that are both too bulky and too expensive as temp sensors so you will probably need to build your own custom boards using ATmegas or ATtiny's. I don't know which of the Tinies that can handle the libraries for the wireless modules. Haven't used ATtiny myself.
There are several options for displaying the temperatures on the tablet. I don't know of a ready-made solution that doesn't require programming. Which options you have depends on what kind of tablet you have but you probably don't want to have the receiving Arduino connected directly to your tablet all the time. Do you?
If that's what you want that could be done by using processing for example but that requires Windows/Mac/Linux rather than iPad or Android.
If you add an Ethernet shield you can post the data to some web page that the tablet can read or you can even run a web server on the receiving Arduino.
A simple network based client/server application might work too.
If the tablet has Bluetooth that could be an option for communication between tablet and Arduino.
Use your imagination.
If you have no idea at all how to do any of it you have a big mountain to climb.
I'm currently playing with a PHP-based web solution for logging temperatures from my sensors to a database and graphing them using Gnuplot. Unfortunately I don't have anything finished to offer you.