Field-Programmable Gate Array (FPGA)
FPGAs are semiconductor devices that are based around a matrix of configurable logic blocks (CLBs) connected via programmable interconnects. FPGAs can be reprogrammed to desired application or functionality.
TinyFPGA BX
A TinyFPGA cost around $50
You can buy a TinyFPGA BX from here for £37.50
The TinyFPGA BX is a small FPGA module with all of the components and circuitry required for the FPGA to function taken care of for you. To develop for the board you create a design in your favorite digital design language (Verilog/VHDL, Migen, and Chisel are some popular options). Alternatively, you can use a schematic entry tool like IceStudio. A schematic entry tool allows you to graphically draw a digital circuit to be implemented on the FPGA.
Once you have a design, you can program it onto the TinyFPGA BX module over USB. All the functions your design implements will now be able to interface with the outside world through the module's IO pins.
Driving a VGA Display?! Getting started with an FPGA! (TinyFPGA)