@Jason Powell Could you do it yourself? Yes, you could. Should you do it yourself? No, you shouldn't. When the IRS reviews a cost segregation study the first thing they look at is the qualifications of the individual who did the study. If that's you and you have no construction engineering experience or training in the tax code pertaining to depreciation they'll probably say you're not qualified. In that case they can throw it out without any further review. Here's the rub, it's quite possible that they won't review the study. They simply don't have the manpower or budget to review every cost segregation study. There are so many things the IRS has to do and making sure depreciation is correct is pretty low on their list. Furthermore they'll usually only go after something if it's worth it, so they're looking for the big fish not the little ones.
If the cost is your main problem with hiring a firm you're not looking hard enough. Lots of firms have popped up that will do cost seg for $500-$1,000. There's usually a bit of a do-it-yourself aspect paired with some proprietary software on these types of studies. Not really a great way to do it since these usually rely heavily on statistical sampling and computer modeling which can be quite different from the actual reality of the property. There's also several engineering firms that have lowered their prices to be more competitive with these software firms.
The main problem with doing it yourself is figuring out what qualifies for accelerated depreciation and what doesn't, and then figuring out the cost basis for each asset. There are hundreds if not thousands of individual assets in a building, and it's usually not cut and dry if something qualifies or not. There's a six part test used to determine if an asset qualifies, the cost books recommended by the IRS are huge, expensive books ($250-$800+ books or online copies usually around 1,000 pages or more) and then everything needs to be adjusted for the location and rectified with the total cost of the property. There's a reason for the high cost of having it done right by an engineer, it takes a lot of time and work (usually 30-250+ hours) and engineers don't work cheap. I've seen many experienced CPAs try to do cost seg (no offense to the many wonderful CPAs here!) and half the depreciation schedule is wrong. Out of tens of thousands of depreciation schedules we've reviewed we've never seen one that was 100% correct, even from big 4 accounting firms with cost segregation departments. It's unlikely you'd be able to do much better without relevant expertise.
All that being said there's nothing stopping you from doing it yourself. The IRS doesn't have any set qualifications or licenses required to do cost seg, but they assume cost seg is only done by individuals with knowledge of construction, construction techniques, design, estimation procedures and the tax code i.e. construction engineers or architects trained in cost seg. They say a study done by a construction engineer is generally more reliable than a study done by someone with no engineering experience. You'll save a few thousand dollars and likely get many thousands of dollars in tax benefits. If the IRS decides to look a little closer you'll likely have to give back all those benefits and have penalties, fees and interest to deal with. But they're probably not gonna look closer. So it's a roll of the dice, you'll have to decide for yourself. It's not a good idea, but lots of people do it with no problems.