Congratulations on your big step with getting your first prescriptions! And a big welcome to Susan's.
We can't give medical advice or dosages here, but many sisters have been on spiro or another androgen blocker prior to starting an estrogen. It will give you the benefits of reducing testosterone production, but your estrogen levels will just be your body's background level produced by your adrenals and fat cells.
If cost is your main obstacle, there are generic forms of estradiol that are considerably less expensive than name brand estrace, usually about half. Also, if you live in a country like the US that has compounding pharmacies and where self-administered injections are legal, you can get a prescription for an injectable form of estrogen (which can often bring your cost down to less than $10 per month).
Going off of estrogen usually is not a health crisis - natal women experience drop offs in their estrogen levels every month of their cycle - but it can affect your mood and can be discouraging as a perceived setback to your transition progress. Many ladies find that they adjust their priorities so that their HRT gets paid for before anything else, because it benefits them that much, but everyone is different.