you can just use a strip of plywood or MDF, and attach it to the workpiece using spring clamps
pro — the cheapest option
con — a strip of engineered wood is going to be a fair bit heavier than aluminum, so I will probably use this only for the shortest straight edges
pro — other than the small complication of making sure one side is very straight, the strip of wood is essentially disposable, so if you accidentally cut into it, it's not a big deal
you can buy a 90° angle of aluminum from a metal supply place, and attach it using spring clamps
pro — the lightest weight
pro — I especially like the 90° angles that are ~2" wide and ~½" high, since the width provides ample room for clamping, while the short height is just enough to brace a hand-saw or power router against (when buying in larger lengths, it can save a lot of money to buy the absolute minimum dimensions that you need)
con — long pieces of metal (≥ 1 m) tend to cost a LOT for shipping, even for very light pieces, so you will probably be incentivized to find a local metal supply house that you can pick it up from, instead of having it shipped from an online store
pro — It can be very challenging to find T-slot material that's longer than 48", or to find self-clamping straight edges longer than 50", but metal supply places can sell you pieces that are even longer than 107" (especially if local pickup works for you)
if you have T-track that's compatible with one of these fixtures, you can use it in combination with that T-track to make your own self-clamping system: