One thing you can do to advance your situation it to get a bag the net type work pretty good from the grocery store the produce comes in. Get a box of ceramic rings /filter media ($12-16) and hang them in the tank in the bag next to the intake of the filter.
You can also add more surface for BB by adding a sponge filter add on - or prefilter filter sponge around the intake and all the foam nooks and crannies will develop BB.
This way you will be adding additional value to the cycle of the new filter or tank to maybe even have it ready and fully functional when you do get a new set up.
You can look for a excellent condition used tank / set up, just make sure to know your best prices for new stuff so you don't get taken. Just because someone else paid $400 for something doesn't mean you need to when you can get it one sale for $250. (those are just numbers pulled out of the air for demonstration purposes,
)
Some times people give away older, slightly scratched or unwanted tanks, especially 55G (48" long) since they are so huge it is inconvenient to store them when people move and after awhile sometimes they are just changing life situations and need to do something else. You may want a nice tank but can get a less than perfect one sooner while still saving for a nicer one.
Same with a variety of filters and substrate, etc. so you can know ahead of time when you stumble on a great deal new or used.
For that matter you may