If you don't want spend money don't bother racing , if you get the race bug
It's going to cost you , you will want the best of every thing you will want spares you will want tyres , why ... Well you don't want to enter a race and have some thing fail if you can't afford a mechanic you have to it your self ( it a good thing thou) but if you can't do it you self then you need a mechanic that cost $$$$
If you are going to buy a used bike plan a rebuild you never know what you are buying so buy new .
Dirt bike racing is cheap compared to super bikes at about $5000 per race weekend , were DB would be $500 + using new tyres entry fees fuel bla bla bla
Not saying it can't be done cheaper but that's what I would spend