Custom hardware is often not more expensive and often looks better.
8020.com has such a high mark up on joining plates, it makes OpenSimRigs custom plates very competitively priced even though we are making very small quantities at the moment.
For example lets look at two ways to design a complex wheel assembly cross brace
The first example below shows 6 standard pivot joints costing $124.50 in 15 series, from 8020.net.
Now compare that with 2 stainless steel custom plates costing $80 & 4 pivots no arms $8.13 total $113.50.
That is a cost saving of $11.00 using custom hardware, and in my opinion the design looks nicer and will be much stronger and more rigid.
Custom plate materials.
Aluminium is the up industry standard available typically 1/8" thick.
But you can consider brushed stainless steel in 14 gauge thickness, because it's stiffer, it's laser cut to perfection, the edge is polished after cutting and looks really awesome. We have all seen how brushed stainless is used in high end kitchen appliances. 14 gauge is about 4 or 5 times thicker!
Custom parts can also be cut from mild steel to save a little and if you want to apply some colour to you rig, mild steel parts can be easily sprayed at home or taken to local a powder coating specialist.