I have a 4' wide raised bed with 16' metal cattle panels held up on T-posts (one T-post every 8'). The bottoms of the panels are about 14-16" off the ground, IIRC. That puts the top of the panels close to 6', and as I am a short person, that's about as high as I can reach. [Some people cut the panels in half and use them vertically, which would be 8' tall but only about 9' wide.] I have access to both sides, and can plant occasional herbs on either side of the row. The holes in the panels are roughly 6 x 7", IIRC.

I weave the young stems in and out of the openings, and as needed use the round vine clips, both as training and to hold vines that need support. [I prefer the red vine clips, but some of the white ones are okay; the green ones I've used don't stay closed, so I don't recommend those. I never remember where I've bought the good ones, so do a Google Images search.]

I trim very few suckers. Plants are 4' apart. You could trim half the suckers and plant at 2 1/2 or 3' apart. But remember that too dense and you're more likely to have fungal problems (possibly contributing to why I had Late Blight in 2009, but not related to last summer's LB).

Stock panels are something you find in an agricultural or semi-rural area. There are various types (cattle, hog, etc.) and sizes, usually 16' long and various heights (usually some inches more than 4'). What matters most is the size of the holes: you don't want tomatoes to be trapped, and you want to be able to reach through the holes and pull large tomatoes through, particularly if you can't walk on both sides of the trellis.

The panels will last forever.

An alternative is concrete reinforcement wire (CRW). It is less expensive (per foot, but you have to buy a lot of it) and it rusts. However, from what I've read here, it will probably last you a couple of decades if you don't leave it lying on the ground. I believe it is 5 or 6' wide. [This is what is generally used for homemade tomato cages.]

Another alternative is the Hortonova netting from Johnny Seeds:
http://www.johnnyseeds.com/c-225-trellis-clips-twine.aspx
[Note the white vine clips on the same page -- and there are brown compostable clips on the second page: never saw those before.]

I set up some of the Hortonova last year, but my tomatoes got LB before they did any climbing. T-posts every however-often, with the yellow plastic clips (for electric fencing) snapped on at the top of each T-post, then the netting hanging from the clips, and finally a strong cord through the top of the netting and attached to each clip, to help support the weight. It would probably be a good idea to weave cord through the net up a few of the T-posts, so the wind wouldn't try to uproot the vines. Guy wires at the ends of the row, if needed.

You might also be able to find white knitted nylon netting in 50 or 60' lengths (maybe 6' wide) in some of the major veggie seed catalogs. It's good stuff and lasts multiple seasons. I don't know if this would support tomatoes, as I've only used it for a late planting of small gourds, very tall peas, and cukes.

Try searches on this forum (and maybe the veggie forum) for "trellis," or "support," or "Hortonova."

Another possibility is the standard Florida-weave, which you can find in searches also. You'll need many strong posts set deep, as well as a whole heck of a lot of cord that doesn't sag.

I am wondering how this has worked out for anyone who has tried it. Any photos you can share?