motherboards depending on where you get it from and which one you need for it can run anywhere from $40-$80 ,pwerboards are only like $10 tops, a new LCD $20-$25, battery depending on where you get it from $10-$30 analog stick $3
your best bet would be to try to look on craigslist or ebay for some broken psps and use them as parts for it, i just got a nice working TA-079 motherboard for someone's psp off ebay for $49.99 with free shipping so check that out oh and if you can try to find a original green powerboard cause the blue phat powerboards suck just about every blue one i have seen or gotten has a defect in it like missing LEDs or a couple home row buttons don't work(just suggesting a new powerboard cause you said your soldering skills weren't that good and its a tiny switch to solder) good luck with it