How hard is it to do your own back taxes?

I recently discovered that I should have been filing taxes in America all along...I contacted an ex-pat tax service who after hearing my case assured me I was well under the income bracket and wouldn't owe anything so I shouldn't worry, and then told me she could file them for $400.00 per missing year.

Is this really worth it? Or can I figure this one out myself? All is above board with my visas etc (ILR), I am unmarried and work part time and pay UK tax. I just want to get this sorted out ASAP, but am really loathe to pay someone for what I might be able to do on my own.

(After all I managed my visa's without an immigration lawyer...surely I can manage this?)

Any help on what forms or who to contact would be most appreciated!

You have to take into account that under current IRS policies you would have to prepare up to 6 years US tax returns, forms 1116, 2555, 1040, Schedule B etc plus TD F 90-22.1s.  Penalties for the TD F 90-22.1 forms alone are a minimum of $10,000 per year so it would pay to get an expert in IRS reasonable cause requests.

The complexity of the forms will depend on such things as UK savings and investments, pension plans, amounts of income, kinds of incomes and deductions etc.