I did a project here on GAF a few months ago, it was to create a custom payment gateway for the joomla virtue mart application, I've finished this and it works ok with joomla, however we have not tested this so their could be problems getting it to work.
The project will consist of making this payment gateway work, you will need to test and debug and problems, if problems occur you should fix them, I do not think their will be any problems but Im busy on another project to be able to do this and my client wants this doing last week.
The payment gateway is realex, all code has been created so your job may be 5 minutes or may be an hour depending whether it works straight away or not.
Questions via PM
I need this done straight away and have a low budget Im afraid, you must be able to follow instructions written in English plus write English very well or you will not be considered for this project.