Planning first engine build, need help

The title says you're planning your first engine build but you end up with you're spending no more than $800? I'm lost
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Planning a first rebuild i guess is a better title. Never done this before, is an $800 budget too low? I can raise it but how much should it be to freshen up an old slant? Dont want cost to exceed value of the car or else id just swap something beefier in, so i guess 1500 is my hard budget, for 2000 i can buy a 318 and transmission or another car