Traditionally, gas has always been cheaper than oil, but who knows now prices are fluctuating so rapidly. Oil has to be bought in advance, which must be costly and doesn't necessarily save in the long run.
As to efficiency, gas and oil are pretty much equal.
I can't say I have ever seen an aluminium radiator and Iron rads are really only for decorative use, and the outputs can be difficult to balance to room size.
Last year 64% of the questions asked in our forum were answered within our DIY project pages at www.diydoctor.org.uk/projects.htm The project pages are now separated alphabetically and your answers are accompanied by diagrams and the ability to see, and buy, the tools and/or required to complete your project. Use our search box to look for your answer and save a great deal of time and money!