You are going to have a lot of work with that truck. It is missing 3 drive shafts, with another possibly broken. Center diff need a top plate. Front shocks missing. Front body mount broken. I don't know what it is, but it has a AE look to it to me. for sure, it started life as a nitro model, then converted to brushless. You may google pics of the AE RC8T and see if it matches.
As for budget power, one cheap option would be to pick up a Arrma BLX185 ESC and motor for about $120 off the ebay kit breakers. To get cheaper than that, you would need to look at the GoolRC/Surpass/Racerstar combos, but those ESCs often don't work out of the box. But if you get a good one, they are decent, so long as you don't get them wet.
For a servo, look at the JX servos - they have some decent servos for < $20. This one is $12, 20kg, and .16s at 6v.
https://www.banggood.com/JX-PDI-622...=detail-bottom-alsobought__1&cur_warehouse=CN
What is your total budget for this build? Less than $500, I am guessing.