Crash, transitioning can be very expensive, but sometimes the best affirmations are easily attainable. There is always a way to transition, sometimes you just have to get a little creative. For the record I'm a Graduate Student at a state university, I made less than $10,000 last year and most of my costs of living come from student loans.
When my next major step is out of reach, I find a smaller step that I can attain. I'm living full-time as a man after less than a year, and I've only spent about $1000. That includes travel to doctors for surgical consultation, T, binders and STP's. Most of what I needed was actually the least expensive option. I use $10 underarmor shirts to bind rather than $30 binders but even those were cheaper than bras. When I couldn't get started on T immediately I spent $12 at walmart to get a pair of swim trunks to wear with a black t-shirt. That first swim as me made a world of difference. Second hand/thrift stores are a great place to pick up a new wardrobe without breaking the bank.
And yes, you can stop in the "middle". There is no set point where you magically "finish" transitioning. I told the US state department that I had "completed clinical treatment for sex reassignment". I'm pre-op and on T. I will always be on hormones so there is no "completion" date. I consider all other surgeries to be standard health maintenance care, my transition "finished" the day I could live full-time as a man and had a couple of ID's to prove it. Sure I'll still need a hysterectomy, but genital reconstructive surgery will likely always be cost prohibitive to me. I'm at peace with that, I'm a man with a micropenis, but my penis, my vagina and I get along just fine as we are. I guess you could say that I've stopped in the middle, but to me it's not the middle its the end, and a beginning. The beginning of being able to live as myself for the first time.
If transitioning is what you need to do, there is a way out there, and we're willing to help you find it.
You mentioned being concerned about your mom's reaction, understandable. I thought my mom could handle everything so watching her grieve for the "daughter" she thought she was loosing was extremely hard. But less than a year later she sent me a valentine, the cover read "To My Son". I was so overjoyed that I cried for joy when I read it. The book "Trans Forming Families" edited by Mary Boeneke provides great insight on how families react to someones transition. I've also found it provided a great bridge for my mom & I to talk about what I was going through. It is an emotional read, so be careful to have the time to sort through what it might bring up.
I hope this helps some. Please believe that you can transition, can chose not to transition, live as a man, a woman, or someone in between and all of these are viable options.