We showed at the World Pinto Show this year and had a wonderful time though it was very expensive there and you already know what the local pinto shows cost if you have been showing your big horse. Having shown both, the pinto shows are more expensive. Getting a mini pinto would be the way to go so you could show both at the same shows. Just take your time and find a good competitive mini. Don't hesitate to maybe post on the sale board and consider horses in other states. The minis we are showing with now are from UT, IL, MO and one was bought locally but had come from TX just a couple of years prior. Sellers will work with you on transport and may be willing to meet you halfway - we've done that before. We also were just getting into minis so made a point of finding seasoned show horses with lots of training and experience behind them. It made things easier for us as we figured it all out.
I love showing pinto - I really like the different driving classes they have and next year we plan to do more local (MN,IA) pinto shows because we also have pinto ponies (13H) that we want to get back in the show ring. This year we chose all AMHR shows (they always seemed to fall on the same weekends) and took usually 4-5 minis to each. Seems like the cost for that many was average about $500-$600 a show for entry fees, stalls, shavings. The check for our last show was $711 so it does vary - the shows that offer a set unlimited classes fee tend to be less expensive.
We have not shown AMHA but I get the impression that they are more expensive than AMHR, could be wrong but seems like that is what I've heard. We also have a lot more AMHR shows in our area too.