Not much problem for waterbased inks.
The cheapest would be a 500w halogen lamp. A few quick passes over the shirt should do it. Even with the regular replacement of the tube, it is still one of the cheapest to buy, operate and maintain. A 1500-2000w heat gun should be next. Actually almost anything that produces heat will do. If you have enough drying space you may also consider air drying it(unless you are using longer drying inks).
Less glamorous than a flash cure but gets the job done.
Alternatives to a 2nd hand oven would be electric bbq grill with flat surface
It has a temp setting and timer. Just figure out a way to suspend or afix it inverted. The temperatures won't be as even as a flashcure so you may need to move the garment a few times to ensure even curing. A turbo broiler also got a temp setting.
The cheapest would be a 500w halogen lamp. A few quick passes over the shirt should do it. Even with the regular replacement of the tube, it is still one of the cheapest to buy, operate and maintain. A 1500-2000w heat gun should be next. Actually almost anything that produces heat will do. If you have enough drying space you may also consider air drying it(unless you are using longer drying inks).
Less glamorous than a flash cure but gets the job done.
Alternatives to a 2nd hand oven would be electric bbq grill with flat surface

It has a temp setting and timer. Just figure out a way to suspend or afix it inverted. The temperatures won't be as even as a flashcure so you may need to move the garment a few times to ensure even curing. A turbo broiler also got a temp setting.