I think you are much better off with a computer. Since price is an issue, get a wrist mounted model and then have your SPG separate and attched to your first stage on your regulator. Besides the SPG you are still going to need some type of depth gauge and a bottom timer or watch. When you add the price of all that together you have just about paid for your computer.
Are you Nitrox certified? If not, you can pick up air computers for very little money these days.
If you are, you definately want a computer because you will in all probability not be using the manual nitrox tables to plan your dives before you go in the water.
If you plan to use the manual air tables and not use a computer, remember the following facts:
you will be greatly penalized on your bottom time because with the manual tables you have
to plan then entire dive as if it was your deepest depth. The computer will be computing
your multi level dive which is what you are actually doing.
you will have to plan your dive before entering the water and carry a slate or some way to
write down the information you need to know so you won't forget it. Then you can not
deviate from your dive plan or your planning is no good, especially if you are doing more
dives during the day.
Are you Nitrox certified? If not, you can pick up air computers for very little money these days.
If you are, you definately want a computer because you will in all probability not be using the manual nitrox tables to plan your dives before you go in the water.
If you plan to use the manual air tables and not use a computer, remember the following facts:
you will be greatly penalized on your bottom time because with the manual tables you have
to plan then entire dive as if it was your deepest depth. The computer will be computing
your multi level dive which is what you are actually doing.
you will have to plan your dive before entering the water and carry a slate or some way to
write down the information you need to know so you won't forget it. Then you can not
deviate from your dive plan or your planning is no good, especially if you are doing more
dives during the day.