Baker Ross have plain cotton tote bags quite cheap. Or how about buying cheap cotton, dyeeing it and then getting sewing?
Could you sell the surplus at a local craft fair/school fete? I have just tie-dyed all the spares left over from t-shirt painting at dd's birthday parties and am hoping that folks will stump up a couple of quid for that 'just off to Glasto' look!
I'll second the tie-tye baby gros/vests. I saw some in GAP a few years ago and they were £12 each! We had a tie-dye session and did the boys pants, they looked very cool.
how about muslin cloths - knickers/pants/socks -
tote bags - pillowcases - cushion covers?
Oooh and plain linen tote bags look fab too. We did this at craft club at school and the girls loved them.
Babygrows are a great present as they look unusual and funky. I also did my DSis some maternity tops with a nice big circle on the bump!
Also i have done curtains in the past - hessian type ones for my conservatory.
Addictive isn't it? There's a joke in my house that if you stand still too long i will tie dye you.
Do t-shirts as presents for other people. Long-sleeved ones for people who don't have summer birthdays.
Also baby vests, and sleepsuits as gifts.
Nappies?
I'm tempted to try dyeing wool for knitting.
We bought some cheap t-shirts from tesco to tie dye yesterday and we've all really enjoyed the process and want to do more, but don't want to end up with millions of tie-dyed t-shirts

Is there anywhere online that sells a kind of collection of stuff to tie-dye - cloth bags, t-shirts, napkins etc.?
Or does anyone else have any ideas for things to dye that we'll actually use?
Going to do some of DH's old work shirts for painting aprons, but that'll only be one dyeing session.
Hoping to keep it low cost too.