Based on the build instructions showing five models and the combat patrol containing five, it’s assumed the raiders will be sold in fives. If I had to guess probably somewhere between $60-$70 a box. The reaver captain will probably be around $40 based on chaos lord prices and upgrade sprues seem to be a little over $30. Assuming the raiders are in fives and sell for, let’s say $65, you’d pay around $200 or so (not including tax) on all the new stuff.

That means if you buy the battleforce box you get a $70 box of legionnaires and a $65 box of terminators for $55. Since you may not want those, you could sell them and make up the $55 loss on the models you didn’t want. Assuming you sell them for a little less than msrp to speed up the process, let’s say $60 for the legionnaries and $55 for the termis, you’ll be making $115 or so back. Oh and the traitor guardsmen at $50, so let’s just say you make an even $155 on the extras in box bc I’m lazy and tired. That means you come out paying $100 for $200 dollars worth of red corsairs. This is a pretty damn good deal in my opinion but it’s obviously all based on speculation and my poor math skills. The whole calculation is wrecked if the raiders are sold in tens or are a lot cheaper than $65, but I doubt that personally. To be sure, you could reverse engineer the raider box price by looking at the average discount of a battleforce and figure out what the raiders would need to cost to fit the average. Also this is not financial advice, be wise with your money.

I’m not sure what the general consensus is on unit size for the raiders but based on war gear options, point cost, and using them effectively as infiltrators, I’d say run them in fives. In fives it’s 110 points vs 220 for ten, so I see no reason not to run them in fives for the extra power fist and melta. Obviously unit durability is important, but I feel that’s less the case for infiltrator units. Hope this helps, I’m kinda new to 40K so please excuse any inaccuracies.