I just designed the frame for my custom laser build. I did a comparison of McMaster-Carr and Misumi, on a much smaller structural frame project - the frame to support the tool rack for my CNC milling machine conversion. IMO....
McMaster-Carr is more expensive on extruded aluminum framing supplies. My very simple little project was about $190 from McMaster-Carr and about $150 from Misumi, although the Misumi version had a 45 degree bracket instead of the clever adjustable angle bracket, but the Misumi version included a significant number of extra slide-in nuts for future projects. Those are goofy expensive at McMaster-Carr. They sell them in packs of four, including the screws. I found Misumi's ordering system to be goofy. It's impossible to find anything on their website. I was able to find the relevant part of the online PDF of their printed catalog and browsing that was a lot easier. Still not convenient, but I could actually assemble an order that way. It was laborious, because the PDF had no links and I can't copy text out of the PDF, so I had to memorize a part number, click over to another browser tab, and type it in to the Misumi parts ordering page.
Misumi does offer a lot more options than McMaster-Carr. If you want something weird, Misumi is generally a better place to find it. They offer black anodized extrusion, for example. More options is a mixed blessing. My frame is fairly simple, and a lot of the Misumi options looked the same and I had a hard time knowing which part I wanted. Shopping is a lot easier at McMaster-Carr. I'm cheap, but I was leaning toward ordering aluminum extrusion framing materials from McMaster-Carr, because the Misumi ordering process was killing too many brain cells. I don't want to make a list, submit a request for quote, get the quote, order it, wait a week for them to ship my stuff and another week to receive it. That's exactly what happened with my ORD Bot parts order from Misumi. McMaster-Carr ships orders placed by 6PM the same day and I have it the next day for a very reasonable UPS Ground shipping charge. I love that.
I've decided to use 1.25" square fiberglass tubing from McMaster-Carr for the frame on my laser. It's about one third the cost of aluminum extrusion, considering the expensive fasteners for the extruded aluminum. For more details on this material and my decision to use it, check out my laser build log.
http://www.buildlog.net/forum/viewtopic.php?f=16&t=1506&p=15105#p15105I did encounter the same UPS VS Freight issue when deciding which fiberglass tubing to order. I could get 24 of the 5' lengths (MC#8548K42) via UPS, or I could get 12 of the 10' lengths by motor freight. The 10 foot pieces were about $40 cheaper, but the trucking freight was $105 to the local depot where I'd pick it up, as opposed to $26 by UPS to my door. It's a little more complicated, as I'd get a better yield with less scrap when cutting from the longer pieces, but I think I'd have enough either way. I'd just have more good pieces left over for the next little project if I started with the ten foot pieces. I decided to go with the shorter pieces by UPS, because I didn't feel like dealing with a trucking company. UPS is a known quantity.
It was nice being able to call McMaster-Carr and get a shipping quote for both options in about a minute. Contrast that with the Misumi quote and surprise process. Ugh. Misumi extrusion is less expensive, but there is such a thing as a false savings. I decided that my brain cells are more valuable than spending a couple of hours saving a few dollars with Misumi. If their order process was as convenient as McMaster-Carr and they had cheap next day delivery, I'd be ordering a lot of stuff from Misumi. Then again, if my grandmother had wheels, she'd be a wagon.