If you buy parts at 'shop cost' versus scrounging closeout, overstock, and pull-a-part sales you'll pay triple, quadruple, or more what the average board member does. Garages pay $80/set (but charge lemmings $125) for the same accel plug and wires we buy for 25 cents/plug and $8/set wires.
The real issue with a ls type swap is unless you custom build your own harnesses, and weld/fab custom mounts, etc yourself, there's isn't a big "shop discount" on those parts the way there is doing an oil change or brake job. Even then, the savvy hobbiest pays 1/3 or less what a shop does - shops get negotiated price, flat, and don't call 40 vendors, hunt closeouts, and horsetrade swap meets.
I've seen basebones 5.3s pulled from wrecked impound trucks swapped in for less than $2k. And they run like it. Work, yes, done "right"? Not so much. I'd be surprised if they worked 6 or even 3 months later without issues
Not saying you can't do it, but, buy your own parts (cheaper in the long run), make a budget (then triple it), and, word to the wise.... friends and business generally don't mix. Inevitably things come up if the 'partnership' goes on too long that leave bad feelings. Or worse.
What if he buys a new house halfway through your project and doesn't have time? What if he expects you to drop what you want to do for side work for him at a cut rate and you cant/don't want to? What about when the guy who isn't a wiring guru and you are working together and the car catches fire? Whose fault is it, and, who pays? Who pays for tools that break during work? What if you're in assembly, something slip, smashes his hand, and he's out of work for 6 months and in therapy?
I learned long ago, and many times over, it's all well and good to bs over cars with friends, but, don't participate in something you won't accept 100% of the loss for.